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REG. U.6. PAT. OFR 


/  ~—sC INSTRUCTION PAPER 


with Examination Questions 





ee . FIRST EDITION 


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_ Furnace Efficiency and 
_- Flue-Gas Analysis 


1744, 


BASS 


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mo fe SCRANTON, PA. 
‘ {INTERNATIONAL TEXTBOOK COMPANY 
1921 





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FURNACE. EFFICIENCY AND 
FLUE-GAS S ANALYSIS 


_ FURNACE EFFICIENCY OF STEAM BOILERS 


GENERAL CONSIDERATIONS 


oe DEFINITIONS 

edd. The efficiency of a boiler is the ratio of the amount of 
\ heat that it absorbs and uses in making steam, to the amount 
ro f heat furnished to it. The heat that is furnished to the grate 
‘is all the heat contained in all the coal, as fired. But the heat 
_ furnished to the furnace and boiler is that in the coal that is 
. ib urned. If a part of the good coal drops through the grate 


% the boiler and furnace must not be charged with its heat. 


Pi, 2. The American Society of Mechanical Engineers’ Com- 
m ittee on Boiler Tests recommends the consideration of two 
Ve eff ficiencies, which are stated as follows: 

| Efficiency of boiler 

: % Heat absorbed per pound of combustible burned (1) 
Calorific value of 1 pound of combustible 


Efficiency of boiler and grate. 
_ Heat absorbed per pound of coal fired (2) 


4 a — Calorific value of 1 pound of coal 


oe _ These two efficiencies necessitate the grate efficiency being 
_ found separately ; that is, 


as ¥ 


Pie, Ber RIGHTED BY INTERNATIONAL TEXTBOOK COMPANY ALL RIGHTS RESIRVED 


- $25 


2 FURNACE EFFICIENCY ok 


bo 
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Bi beney operate Pounds of saith burned (3) 
Pounds of combustible fired 





Later recommendations give the following efficiencies: 


Efficiency of boiler, furnace, and grate 
_ Heat absorbed per pound of coal fired 





Calorific value of 1 pound of coal 
_ Heat absorbed per pound of combustible fired 


4 

Calorific value of 1 pound of combustible 4) 
Efficiency of boiler and furnace 

_ Heat absorbed per pound of combustible burned (B) 


Calorific value of 1 pound of combustible 


3. It is difficult to determine the actual efficiency of a 
boiler alone, as distinguished from the combined efficiency of 
boiler, grate, and furnace. ‘This is owing to the fact that the 
losses due to excess air cannot be charged to either the boiler 
or the furnace, but only to the apparatus asa whole. Attempts 
have been made to divide the losses proportionately between 
the boiler and the furnace, but without success. General 
practice, however, has established the use of the efficiency 
based on combustible as representing the efficiency of the 
boiler alone. When that efficiency 1 is used, its exact meaning 
should be understood. 


4. To illustrate the application of the statements made, 
consider the following data obtained during a boiler trial: 


Steam pressure, gauge, in pounds per square 


INCH yi toga ak Ae se ee ee 180 
Feedwater temperature...................5 170° F. 
Total weight of coal fired, in pounds........ 17,300 
Percent) moisturein coals. e. ve ce eee Se 
Total ash and refuse, in pounds............ 2,300 
Total water evaporated, in pounds........ _.. 152,000 
Per cent. moisture in steam.. —s 6 


Heat value per pound of dry en in fae T. U 13,500 
Heat value per pound of combustible, in 


~ 


>. 


e 


80406 


[2] 


§ 25 AND FLUE-GAS ANALYSIS 3 

The actual evaporation corrected for moisture in the steam 
is 152,000 — (152,000 x .006) = 151,088 pounds. Equivalent 
evaporation from and at 212° F. is 151,088 x 1.096 = 165,592+ 
pounds. Total dry fuel is 17,800 (1—.03)=16,781 pounds. 
Evaporation per pound of dry fuel from and at 212° F. is 
165,592+ 16,781=9.87 pounds, closely. Heat absorbed per 
pound of dry fuel will be 9.87 X966.1=9,535+ B. T. U. 
Therefore the efficiency of boiler, furnace, and grate, by for- 
mula 4, Art. 2, is 9,535+13,500=.706+, or 70.6 per cent.; 
the total combustible burned is 16,781 —2,300 = 14,481 pounds; 
and the evaporation from and at 212° F. per pound of com- 
bustible is 165,592 + 14,481 =11.44 pounds, closely. There- 
fore the efficiency of boiler and furnace, based on combustible 
burned, by formula 5, Art. 2, is (11.44966.1) + 15,350 
=.7199-+ =71.99 per cent. 


5. Boiler efficiencies will vary over a wide range, depending 
on a variety of factors and surrounding conditions. With 
coal as the fuel, an efficiency of 82 per cent. has been obtained 
and it has been known to go below 50 percent. The difference 
between the efficiency obtained in any case and perfect efficiency 
(100 per cent.) includes the losses that occur, some of which 
are unavoidable. 


HEAT LOSSES 


6. The various heat losses that occur may be stated as 
follows: 

Loss from fuel dropping through the grate. 

Loss due to unburned fuel carried away in small particles up 
the stack by the intensity of the draft. 

Loss due in heating the moisture in the fuel from atmospheric 
temperature to the boiling point, which at sea level is 212° F., 
to evaporate it at that temperature and to superheat the steam 


- so formed to’the temperature of the flue gases. This steam is 


just heated to the temperature of the furnace, but as it gives 
up a portion of this heat in passing through the furnace, the 
superheating to the temperature of gases entering the chimney 
is the loss to be considered. 





4 FURNACE EFFICIENCY ‘98-25 


Loss due to the forming of water through the burning of the 
hydrogen in the fuel, which water must be evaporated and 
superheated, the same as the moisture content of the fuel. 

Loss due to superheating the moisture in the air supplied, from 
the atmospheric temperature to the temperature of the flue gases. 

Loss due to heating the dry products of combustion to the 
temperature of the flue gases. 

Loss due to incomplete combustion, when the carbon burns 
to carbon monoxide, CO, instead of to carbon dioxide, COs. 


7. Elaborate tests would have to be made if all the items 
just enumerated were to be determined accurately. In practice 
it is customary to compute the loss due to heating the moisture 
in the fuel from the atmospheric temperature to the boiling 
point, which at sea level is 212° F., evaporating it at that tem- 
perature, and superheating it to the temperature of the flue 
gases, by the following formula: 

A=W[(11—-)+L+.48(T — T;)] 
in which W=moisture in coal, in per cent., expressed decimally; 
t=temperature of air in boiler room; 

T =temperature of flue gases; 

T,=temperature of boiling point of water, tefl 
taken as 212° F. unless otherwise stated or 
required; 

L=B. T. U. necessary to evaporate 1 pound of water 
at boiling point to steam at atmospheric 
pressure; 

48 = specific heat of superheated steam at atmospheric 
pressure and at temperature of flue gases; 

A=heat loss, in B. T. U., per pound of coal. 

EXAMPLE.—A quantity of coal contains 2 per cent. of moisture. The 
temperature of the air in the boiler room is 80° F., the temperature of boil- 
ing water at the pressure of the atmosphere at sea level is 212° F., the 
latent heat of steam at atmospheric pressure is 966.1 B.*T. U., and the 


temperature of the flue gases at the last pass in the furnace setting is 500° F. 
What is the loss, in B. T. U., per pound of coal? 


SOLUTION.—Applying the formula, 
A= 02 X[(212—80) + 966. 1+.48 X (500 —212)] = 24.73 B. T. U. per Ib., 
closely. Ans. 


s 


§ 25 AND FLUE-GAS ANALYSIS 5 


8. The heat loss due to the heat taken away in the steam 
by the burning of the eee uk in the fuel is expressed by the 
following formula: 


A=9H[(T:—-1)+L+.48(T— 7] 


in which H=percentage, by weight, of hydrogen, expressed 
decimally, and the other letters have the meaning givenin Art. 7. 

Where an ultimate analysis of the fuel is not given, this item 
is generally considered as part of the unaccounted for loss. 

EXAMPLE.—A certain coal contains 5 per cent. of hydrogen, the temper- 
ature of the air in the boiler room is 80° F., the temperature of boiling water 
at the pressure of the atmosphere at sea level is 212° F., the latent heat 
of steam at atmospheric pressure is 966.1 B. T. U., and the temperature 
of the flue gases at the last pass in the furnace setting is 500° F. What is 
the loss, in B. T. U., per pound of coal? 

SoLuTION.—Applying the formula, 


A=9xX.05 X [(212—80) +966.1-+.48 x (500 —212)] 
=556.35+ B. T. U. per lb. Ans. 


9. The heat loss due to the heat taken away by the dry 
chimney gases depends on the weight of gas per pound of fuel, 
which weight may be determined by this formula: 


_11C0,+80+7(CO+N) 1) 
3(CO;+C0) 


in which W=weight of flue gases per pound of carbon; 
CO.=percentage of carbon dioxide, as found from a 
flue-gas analysis; 
O=percentage of oxygen, as found from an analysis; 
CO=percentage of carbon monoxide, as found from 
an analysis; 
N= percentage of nitrogen, as found from an analysis; 
C=percentage of carbon, by weight, in dry fuel, as 
found from an ultimate analysis. 


All percentages are to be expressed decimally in this formula. 


ExamPte.—A flue-gas analysis gave the following values: Carbon 
dioxide, CO2z, 14 per cent.; oxygen, O, 4 per cent.; carbon monoxide, CO, 
.2 per cent.; and nitrogen, N, 81.8 per cent. The percentage of carbon, by 
weight, in the coal used was 78. What was the weight of gas per pound of 
coal? 


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§ 25 AND FLUE-GAS ANALYSIS 7 


_ SoLutTion.—Applying the formula, 
_11X.144+8X.04+7 x (.002+.818) 
iy 3X (.14+.002) 


WwW X.78=13.92— lb. Ans. 


The heat loss per pound of dry coal is given by the formula 
A= .24W,(T —t?) (2) 
in which .24=specific heat of chimney gases; 
W,=weight of dry chimney gas per pound of dry coal; 
T =temperature of flue gases; 
t=temperature of air in boiler room; 
A=heat loss per pound of dry coal, in B. T. U. 
EXAMPLE.—In a given case, the weight of chimney gas per pound of dry 
coal is 13 pounds, the temperature of the flue gases at the last pass is 


500° F., and the temperature of the air in the boiler room is 80° F. What 
is the heat loss per pound of dry coal? 


SOLUTION.—Applying the formula, 
A =.24X13 X (500—80) =1,310.4 B. T. U. per lb. Ans. 


10. <A convenient, but approximate, method of calculating 
the percentage of heat lost in dry flue gases when the percentage 
of CO2 only is known is that given in the chart, Fig.1. Thecurve 
shows the constant to be used in the following formula. The 
constants appear at the left side of the chart and are designated 
as values of Y in the formula: 

rome) 
in which Q=percentage of heat lost; 
Y =constant found from chart; 
T =temperature of flue gases, in degrees F.; 
t=temperature of boiler room, in degrees F. 

The constants are derived from a complicated series of cal- 
culations, a knowledge of which is unnecessary to obtain results 
from the chart. 

The chart is based on theoretical conditions, and on the 
assumption of complete combustion, although with variable 
' quantities of excess air, as indicated by the CO, values. The 
results obtained by its use may vary from those obtained by 
formulas that contain complete data; but in cases where only the 
percentage of CO; is known, it is better to make use of the chart 
and obtain the approximate loss, than to neglect it entirely, 


8 FURNACE EFFICIENCY § 25 


EXAMPLE.—In a certain boiler plant, the avérage carbon dioxide, COz, 
in the furnace gases is 10.3 per cent., the average temperature of the gases 
in the flue leading to the chimney is 450° F., and the temperature in the 
boiler room is 80° F. What is the percentage of heat lost, assuming the 
gases to be dry? 


SOLUTION.—Referring to the chart, locate 10.3 per cent. of dioxide, COs». 
in the horizontal row of figures at the base. Follow vertically to the inter. 
section of the curve, then follow the horizontal line at that point, to the 
left of the chart until the vertical row of figures is reached. In this case 
the number is .04, which is the value of Y in the formula given. Substi- 
tuting the known values in the formula, 


Q=.04 (450—80) =14.8 per cent. loss. Ans. 


11. The heat loss due to incomplete combustion of the 
carbon content of the fuel, burning it to carbon monoxide, CO, 
instead of to carbon dioxide, COs, which latter condition is 
necessary to complete combustion, is given by the formula 


10,150 CO 
CO2+CO 


in which C=per cent. of carbon in coal as found from an 
ultimate analysis; 
CO=per cent. of carbon monoxide by volume, as 
found from a flue-gas analysis; 
COz=per cent. of carbon dioxide by volume, as found 
from a flue-gas analysis; 
10,150=number of heat units generated by burning 
1 pound of carbon contained in carbon mon- 
oxide, to carbon dioxide; 
A=heat loss per pound of dry coal, in B. T. U. 


A=CX 


All percentages are to be expressed decimally in applying 
the formula. 


EXAMPLE.—A flue-gas analysis gives the values of CO, as 14 per cent. 
and of CO as 2 per cent.; the percentage of carbon in the coal used, as 
found from an ultimate analysis, is 78. What is the heat loss per pound 
of dry coal? 


SOLUTION.—Applying the formula, 


10,150 x .002 
Atala me (| gpa B. T. U. per lb. Ans. 


A=.78 
* -14+.002 





§ 25 AND FLUE-GAS ANALYSIS 9 


12. The heat loss due to unconsumed carbon contained in 
the ash cannot be calculated unless an analysis of the ash has 
been made. From this analysis the heat loss, in B. T. U., per 
pound of dry coal supplied to the boiler, is usually computed 
on the assumption that all the combustible found in the ash is 
carbon. The heat loss per pound of dry coal, in B. T. U., is 
then obtained by multiplying together the decimally expressed 
percentages of ash, and carbon in the ash, and 14,600; the figure 
just given is the number of B. T. U. in 1 pound of carbon. 
The formula is as follows: 


A=ac 14,600 


in which A =heat loss per pound of dry coal, in B. T. U.; 
a=percentage of ash and refuse from dry coal, 
decimally expressed; 
c=percentage of carbon in ash and refuse, decimally 
expressed. 


EXxAmPLE.—The analysis of a sample of ash shows 15 per cent. of com- 
bustible matter, all of which is assumed to be carbon. The boiler test 
showed that 10 per cent. of the total dry coal fired was ash and refuse. 
What is the heat loss, in B. T. U., per pound of dry coal? 


SoLuTION.—Applying the formula, 
.10X.15X 14,600 =219 B. T. U. per lb. Ans. 


13. The refuse in furnace ash-pits is usually known as ash; it 
consists of both incombustible matter and unburned and partly 
burned coal that drops through the grates. <A distinction must 
be made between this kind of ash and true ash in coal. The 
former is found by comparing its weight with the weight of the 
dry coal fired in any given period of time, in any given case. 
For example, during a certain boiler test 5,609 pounds of dry 
coal per hour was fired into the furnace, and during the same 
period of time 561 pounds of ash and refuse collected in the 
ash-pit. This 561 pounds of refuse is 10 per cent., closely, of 
- the dry coal fired, but this is not necessarily the percentage of 
true ash in the coal used. 

The true ash in coal is found by an analysis of the coal. 
Analyses should be made by those skilled in that line of work, 
and in places equipped with the necessary apparatus for that 


10 FURNACE EFFICIENCY § 25 


purpose. To find the amount of combustible matter in refuse, 
a sample of the refuse is burned in a crucible with oxygen, a 
Bunsen burner supplying the heat. 


14. When the percentage of combustible matter in a given 
sample of refuse is known, and also the percentage of true ash 
in the coal from which the refuse came, the percentage of coal 
lost is given by the formula, | 

rt ab 
(1—a) (1—b) 
in which A = percentage of coal lost in refuse; 
a=percentage of combustible in refuse, expressed 
decimally ; 
b=percentage of true ash in coal from which refuse 
came, expressed decimally. 

EXAMPLE 1.—A sample of ash refuse from a boiler furnace was analyzed 

and found to contain 29 per cent. of combustible matter. The true ash in 


the coal from which the refuse came was found to be 11.9 per cent. What 
is the percentage of coal lost in the refuse? 


SOLUTION.—Applying the formula, 


oe dt 0552 = 5.52 t., closel A 
= =), == 5. er cent., closely. Ans. 
(1 29) X (17119) : : 





EXAMPLE 2.—A sample of ash refuse contains 36.4 per cent. of com- 
bustible matter. The true ash in the coal from which the refuse came is 
10.5 per cent. What per cent. of coal is lost in the refuse? 


SOLUTION.—Applying the formula, 
.364 X .105 


FOTW anys Oh amie eee get ae tail 
(1 —.364) x (1—.105) 0671 -- + per cen ns 


15. The formula given in Art. 14 does not take into account 
volatile matter that may bein the coal. If from an analysis of 
the coal the fixed carbon is obtained, representing the decimally 
expressed percentage of fixed carbon by d, the formula becomes 


Au? b (d+b) 
(l—a)d 
EXAMPLE.—A sample of ash refuse contains 30 per cent. of combustible 


matter, the true ash in the coal is 10 per cent., and the fixed carbon is 
80 per cent. What percentage of coal is lost in the refuse? 






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Per Cent. Combustible in Ashes 


Fic. 2 


12 FURNACE EFFICIENCY § 25 


SoLuTION.—Applying the formula, 
30X10 (.80+.10) _ 


we OS 0482-4 = 4,82 t. Ans. 
A= 30) X.80 ¥ Pet cont adn 


16. In Fig. 2 is shown a graphic method for obtaining the 
same results as are obtained from the formula in Art. 14. 
The horizontal row of figures at the base of the diagram repre- 
sents the known per cent. of combustible in the ashes, as found 
by analysis. The vertical row of figures at the right-hand side 
of the diagram represents the per cent. of true ash in the coal, 
also found by analysis. The vertical row of figures at the 
left-hand side of the diagram represents the per cent. of coal 
loss. Knowing the per cent. of combustible in the ashes and 
‘the per cent. of true ash in the coal in any given case, the 
per cent. of coal loss may be found by locating the point of 
intersection of these values on the diagram, and following the 
horizontal line to the left, which gives the percentage sought. 

A study of Fig. 2 shows that the higher the percentage of 
true ash in the coal the greater will be the percentage of coal 
loss in the refuse. With the small sizes of anthracite contain- 
ing from 12 to 24 per cent. of ash, the importance of burning 
the fires as thoroughly as possible is clearly shown. A con- 
siderable saving in coal can be made by giving careful attention 
to this matter. | 

EXAMPLE 1.—A sample of ash refuse contains 24 per cent. combustible 


matter, but the amount of true ash in the coal is 14 per cent. What is the 
percentage of coal lost in the refuse? 


_ SoLuTIoN.—On the horizontal line entitled Per Cent. Combustible in 
Ashes, the number 24 is found and this line followed up vertically until it 
intersects the curve 14. These curves represent the true ash in the coal as 
found by analysis and are numbered by the vertical row of figures at the 
right-hand side of the diagram. Following the horizontal line nearest the 
intersection of lines 24 and 14 to the vertical row of figures at the left- 
hand side of the diagram, it is found that this intersection lies between 
5 and 6, accurately 5.2; this represents the percentage of coal lost in the 
refuse. Ans. 


EXAMPLE 2.—A sample of ash refuse is known to contain 30 per cent. 
of combustible matter. The coal loss in the refuse is known to be 7 per 
cent. but the record giving the amount of true ash in the coal is lost. From 
the diagram find the per cent. of true ash. 


§ 25 AND FLUE-GAS ANALYSIS 13 


SOLUTION.—The number 30 in the horizontal row ot figures is followed 
up vertically to the horizontal line numbered 7 at the left of the diagram. 
The curve nearest the intersection of these lines gives the per cent. of true 
ash in the coal, which in this case is 14. Ans. 


EXAMPLE 3.—A sample of coal contains 15 per cent. of true ash and an 
_ analysis of the refuse from this coal shows a coal loss of 10 per cent. What 
is the per cent. of combustible in the refuse? 


SOLUTION.—Horizontal line 10 is followed to its intersection with the 
curve 15; the nearest vertical line gives the per cent. of combustible in the 
ashes, which in this case is 36. Ans. 


17. The heat loss due to unburned fuel carried by the draft 
beyond the bridge wall and up the chimney, that due to super- 
heating the moisture in the air supplied, from atmospheric 
temperature to the flue-gas temperature, and that due to radi- 
ation of heat from the furnace settings and the boiler, may be 
called unaccounted for losses. ‘These losses, in B. T. U., are the 
difference between the heating value of 1 pound of dry coal, 
as determined by analysis, and the sum, in B. T. U., of the heat 
utilized by the boiler and the various heat losses accounted for. 
Or, in per cent., the unaccounted for losses are given by sub- 
tracting from 100 the sum of the percentage of heat utilized 
and the percentages of the various accounted for heat losses. 
The loss due to moisture in the air is small, averaging less 
than one-half of 1 per cent., so it is sometimes disregarded in 
practical work. 


18. The determination of the various heat losses requires 
an evaporative test of the boiler, an analysis of the flue gases, 
an ultimate analysis of the fuel, and either an ultimate or a 
proximate analysis of the ash. After the data has been secured 
from the test and analyses referred to, a heat balance may be 
struck, which shows almost at a glance just where the heat in 
the fuel has gone, and what it has done. 


ILT 168—43 


14 FURNACE EFFICIENCY § 25 


ATR REQUIRED FOR COMBUSTION 


PROCESS OF COMBUSTION 


19. Before fuel can be burned in a furnace, oxygen must - 
be supplied to support the combustion of the fuel. Combustion 
is the rapid chemical combination of two or more substances 
with the production of light and heat. That part of the fuel 
that combines with the oxygen is termed combusttble, and in 
practice is the part of the fuel that is dry and free from ash. 
This includes both oxygen and nitrogen that may be in the fuel, 
although nitrogen is not a combustible element. The prin- 
cipal combustibles in coal and other fuels are carbon, C, hydro- 
gen, H, and sulphur, S, which occur in various combinations 
and proportions in different fuels; carbon, however, is the 
principal one. 

Combustion is perfect when one atom of carbon unites with 
two atoms of oxygen to form carbon dioxide, CO,. Combustion 
is imperfect when the combustible does not unite with the 
proper amount of oxygen; but, when one atom of carbon unites 
with one atom of oxygen to form carbon monoxide, CO, this 
may be further burned to carbon dioxide, COs. 


20. When the air, which supplies the oxygen for combustion, 
passes up between the grate bars in a boiler furnace and under 
the fuel, combination takes place between the oxygen of the 
air and the under layers of glowing carbon, forming carbon 
dioxide, CO;. ‘This gas, in passing on through the upper layers 
of carbon, loses part of its oxygen, and the dioxide, COs, is 
reduced to carbon monoxide, CO, the remainder of its oxygen 
having united with more carbon to form monoxide, CO, also. 
But if sufficient air is supplied at the surface of the fuel, the 
monoxide, CO, will burn to dioxide, CO:, with further evolution 
of heat. If sufficient air is not supplied, the monoxide, CO, will 
pass up the chimney unconsumed, which means a loss that is 
preventable to a great extent. 

It has been found that 1 pound of carbon will unite with 

% pounds of oxygen to form carbon dioxide, COz, and will 


§ 25 AND FLUE-GAS ANALYSIS 15 


evolve 14,600 B. T. U. As an intermediate step, 1 pound of 
carbon may unite with 14 pounds of oxygen to form carbon 
monoxide, CO, and evolve 4,450 B. T. U.; but, in its later 
conversion to carbon dioxide, COs, it will unite with an addi- 
tional 13 times its weight of oxygen and give out the remaining 
10,150 B. T. U. which would otherwise be lost. 


AIR-SUPPLY CALCULATIONS 


21. Pure air is a mechanical mixture of oxygen and nitrogen, 
in the proportion of 20.91 per cent. of oxygen and 79.09 per 
cent. of nitrogen, by volume, and 23.15 per cent. of oxygen 
and 76.85 per cent. of nitrogen, by weight. Different authori- 
ties give slightly varying values, but these proportions are 
generally accepted as being correct. Frequently the values 
are given in round numbers as a matter of convenience: in the 
first instance, 21 per cent. of oxygen and 79 per cent. of nitro- 
gen, and in the second instance 23 per cent. of oxygen and 
77 per cent. of nitrogen. Under actual and natural conditions, 
air always contains other constituents in varying amounts, as 
follows: carbon dioxide, ozone, water vapor, and dust. 

The weight and volume of air depend on the pressure and 
temperature. The specific heat of air at constant pressure 
varies with the temperature, ranging from .236 to .248. In 
practical work .24 is usually employed. 

The following formula shows the relation that exists between 
weight, volume, pressure, and temperature of air: 


PV=53.8T W 


in which P=absolute pressure, in pounds per square foot; 
V =volume, in cubic feet, of given weight of air, in 
pounds; 
T =absolute temperature of air, in degrees F.; 
W =weight of air, in pounds. 


The weight of 1 cubic foot of air at a given absolute pressure 
and absolute temperature is the reciprocal of the volume of 
1 pound of air at the same absolute pressure and absolute 
temperature; that is, it equals 1 divided by the volume in 


16 FURNACE EFFICIENCY: § 25 


cubic feet at the same absolute pressure and absolute 
temperature. 


22. From the formula given in Art. 21 the following for- 
mulas are derived: 5337 W 
VY =—__ (1) 
igs 
EXAMPLE.—What is the volume, in cubic feet, of 1 pound of air at 


an absolute pressure of 75 pounds per square inch, and an absolute temper- 
ature of 575° F.? 


SOLUTION.—Applying the formula, and remembering that 144 sq. in. 
=1 sq. ft., 


53.8 X575X1 
ce NL = 2.84 cu. ft., closely. Ans. 
14475 
53.8 TW 
Pts eee (2) 


V 


EXAMPLE.—What is the absolute pressure, per square inch, of 1 pound 
of air at an absolute temperature of 575° F. and a volume of 2.84 cubic feet? 


SoLuTION.—Applying the formula, 





53.3 X575X1 
= 5.84 =10,791.3++ lb. per sq. ft. 
and, 10,791.38 +144 =74.9+ Ib., absolute, per sq. in. Ans. 
J 
= (3) 
53.38 W 


EXAMPLE.—What is the absolute temperature, in degrees F., of 1 pound 
of air that has a volume of 2.84 cubic feet at an absolute pressure of 
10,791.3 pounds per square foot? 

SoLuTIoN.—Applying the formula, 

_ 10,791.38 X 2.84 


= 575° F., closely. : 
533%1 , Closely. Ans 


Formula 1 may be used for other gases, but with a change in 
the constant. For oxygen, the constant is 48.24; for hydrogen, 
765.71; and for nitrogen, 54.97. 


23. The theoretical amount of air required varies with 
different fuels. Anthracite needs 11.7 pounds of air per pound 
of coal, bituminous coal 11.6 pounds per pound of coal, oil 
14.3 pounds, and wood 6 pounds per pound of fuel. 


§ 25 AND FLUE-GAS ANALYSIS LYé 


Perfect; combustion of fuel in the furnace of a steam boiler 
is not possible with only the exact theoretical amount of air 
specified, because it is not possible to bring each particle of 
oxygen in the air into contact with the particles in the fuel 
that are to be oxidized. This is due to the dilution of the 
oxygen by nitrogen, and also to such factors as uneven thick- 
ness of fire and varying resistance to the passage of air through 
the fire due to ash and clinker. 


24. When there is no fuel bed through which the air has to 
be drawn, as in the case of burning gas or oil, the excess air 
supply may be less than that required for coal. Speaking in 
general, coal will require from 40 to 50 per cent. more air than 
the theoretical amount, or on an average of about 18 pounds of 
air per pound of coal, under either natural or forced draft. This 
amount may vary widely with different furnaces, kind of coal, 
and the manner of firing the coal. Too much excess air must, 
however, be guarded against, for it means an avoidable heat 
loss. ‘Too little air also means heat loss, for then the carbon 
burns to carbon monoxide, CO, and the full heat value is not 
developed. 


FLUE-GAS ANALYSIS 


METHODS OF ANALYZING FLUE GASES 


OBJECT OF GAS ANALYSIS 

25. One means of determining what is necessary to secure 
furnace efficiency is the analysis of flue gases. From such an 
analysis may be learned the amount and distribution of the heat 
losses that may occur, due to incomplete combustion of the 
fuel. The quantities actually determined by a flue-gas analysis 
are the relative proportions, by volume, of carbon dioxide, COz, 
oxygen, O, and carbon monoxide, CO, in the order named. 
But in some cases only that for carbon dioxide may be required. 

The complete combustion of 1 pound of pure carbon requires 
2.67 pounds of oxygen, or 32 cubic feet at 60° F. When the 
gaseous product of such combustion is cooled, it will occupy 


18 FURNACE EFFICIENCY § 25 


the same volume as the oxygen, 82 cubic feet. The carbon 
unites with the oxygen and forms carbon dioxide, CO2; this will 
have the same volume as the oxygen in the original supply of air. 

The volume of the nitrogen when cooled will be the same as 
that in the air supplied, for it undergoes no change whatever. 


26. For the complete combustion of 1 pound of carbon, 
without any excess of air, the gas analysis will show the per- 
centages by volume to be as follows: | 


PER CENT. 
Carboriididxide. 22 Sein 8a: 4 Po be «ak 20.91 
Oxyoen. . fect borings. Sad anerlt Zeek sek. 0.00 
Nitrogen’ Jf. tern OS GF OR Bai) een Dee 79.09 
100.00 


The actual volume, in cubic feet, for 1 pound of carbon and 
the foregoing percentages, will be as follows: 


Cusic FEET 
Carbon CiOxTdes oe ce ne ch eet een ee 32 
OXVPCH ee he eat tee ee act ete 0 
INICPOP Erie. cea neers eee be ane eens en 121 


Air required for the complete combustion of 
1 pound. of canbone., . 4.45. he eh te 153 
Assuming that there is 50 per cent. excess of air, the volume 


will be 1531.5 =229.5 cubic feet of air per pound of carbon. 
The gas analysis will show the percentages by volume as follows: 


PER CENT. 
Carbo. dioxide... 7 epee eee 13.91 
Cae ARR OTUE 90 7 00 201 
Nitrogenia) or ee ue Ate ene Smee 79.09 

100.00 


The actual volume, in cubic feet, for 1 pound of carbon and 
the foregoing percentages, will be as follows: s 
Cusic FEET — 


Carbon lioxide wéste encleus ta eek wre ee 32.0 
OXY Pets crgivtestey Deteiseties apie 16.0 
Nitrogent...oe, 4a paet. ian. biibevetiatiron aaa 181.5 


wa) 
bo 
Ot 


AND FLUE-GAS ANALYSIS tp 


Assuming that there is 100 per cent. excess of air, the volume 
will be 153 X2=306 cubic feet of air per pound of carbon. The 
gas analysis will show the percentages by volume as follows: 


PER CENT. 
Mato tiOxIGG) a 10.46 
(CER RS RENE SPCC i aa 10 if ea 
EST TR Oi EP DD 79.09 
100.00 


The actual volume, in cubic feet, for 1 pound of carbon and 
the foregoing percentages, will be as follows: 


CuBic FEET 
PARDON IMOKId Owl AR weil «aged. ale obs 32 
DK Vee ith. fon heboe ie odd este boa ort 32 
Nisropen sick ty tack) ch-eecdiid tonne! sod uets 242 
306 


27. A study of the values just given shows that the actual 
volume of carbon dioxide per pound of carbon remains the 
same, but that the percentage by volume decreases as the air 
excess increases, no matter what excess of air is supplied. The 
actual volume of oxygen and the percentage of oxygen by vol- 
ume increases with the excess of air, showing that the percent- 
age of oxygen is an’ indication of the amount of excess air. 
The sum of the percentages of carbon dioxide and oxygen is 
the same, 20.91. 

The volume of nitrogen increases with the excess of air; but 
the percentage by volume remains the same. ‘This is due to 
the fact that no change takes place in the nitrogen during 
combustion. The percentage for any amount of excess air 
will be the same after combustion as before, if it is cooled to 
the same temperature. In this discussion the conditions relate 
only to the perfect combustion of 1 pound of carbon. The 
product of imperfect combustion of carbon is carbon monoxide, 
CO, which will occupy twice the volume of the oxygen entering 
its composition. 

If pure carbon were the fuel to be used, the sum of the 
percentages (by volume) of carbon dioxide, oxygen, and one- 
half of the carbon monoxide, must be in the same ratio to the 


—6«f4y 





20 FURNACE EFFICIENCY § 25 


nitrogen in the flue gases as the oxygen is to the nitrogen in 
the air; as already stated, this is 20.91 to 79.09. 


28. When coal is the fuel used, the percentage of nitrogen 
is found by subtracting the sum of the percentages (by volume) 
of the other gases from 100. For example, an analysis gives 
13 per cent. of carbon dioxide, 5 per cent. of oxygen, and 
.5 per cent. of carbon monoxide. The quantity of nitrogen, 
which is the only other gas to be considered in practical work 
of this kind, is 100—(13.0+5.0+.5) =81.5 per cent. 

Nitrogen performs no useful service in combustion, and it 
goes through the furnace without change. It is the chief source 
of heat losses in furnaces, because it absorbs heat, lowers the 
temperature, and dilutes the air supplied. | 

Considering the density of air as 1, that of nitrogen is .9673, 
and its weight is .07829 pound per cubic foot, under atmospheric 
pressure and at 32° F. Each pound of air at atmospheric 
pressure contains .7685 pound of nitrogen, and 1 pound of 
nitrogen is contained in 1.801 pounds of air. 


29. Speaking in general, a high percentage of carbon dioxide 
indicates good combustion and high efficiency, but this is 
true only in the sense that high readings of the dioxide indicate 
the small amount of excess air that accompanies good com- 
bustion. For a full and satisfactory analysis, the percentage 
of carbon monoxide must also be obtained if there is any of 
that gas present. Carbon-dioxide readings alone, are not 
entirely reliable, when it is desired to learn all that is to be 
known relative to the subject. 

As the percentage of dioxide increases, there is a tendency 
toward the formation of monoxide, which may be small in 
quantity, but which nevertheless should be known and taken 
into account. The effect of a small quantity of monoxide, 
even | per cent., present in flue gases, will have but very little 
influence on the quantity of excess air, but such an amount 
would mean a loss of approximately 4 per cent. of the total 
heat in the fuel consumed, due to the incomplete combustion 
of the carbon in the fuel. Thus, it is important that a complete 
analysis be made, showing the percentages of all the gases that 


<7) 


§ 25 AND FLUE-GAS ANALYSIS 21 


are considered, namely: Carbon dioxide, CO2; carbon mon- 
oxide, CO; oxygen, O; and nitrogen, N. 

High percentages of carbon dioxide may be accompanied by 
considerable carbon monoxide and consequent loss; this condi- 
tion is one of imperfect combustion resulting from faulty firing, 
or improper furnace design. 


30. The percentages that are found from an analysis of 
flue gases are usually expressed in terms of volume. Should 
it be required, for any reason, to know the percentages by weight 
instead of, or, as well as, by volume, then these percentages 
may be found as follows: Multiply the percentage, by volume, 
of each gas by the molecular weight of each gas, and add the 
several products together. Then to find the percentage of 
each gas by weight, expressed decimally, divide the product 
of its percentage by volume and its molecular weight by the 
sum of the several products. The molecular weights are as 
follows: Carbon dioxide, 44; carbon monoxide, 28; oxygen, 32; 
nitrogen, 28. 

Examp_e.—A flue-gas analysis shows that a sample contains, by 
volume, 11.9 per cent. of carbon dioxide, .3 per cent. of carbon monoxide, 


7.1 per cent. of oxygen, and 80.7 per cent. of nitrogen.. Convert the 
percentages by volume into percentages by weight. 


SOLUTION.—The product of the percentage of carbon dioxide and its 
molecular weight is 11.9*44=523.6. The product of the percentage of 
carbon monoxide and its molecular weight is .38X28=8.4. The product of 
the percentage of oxygen and its molecular weight is 7.1X32=227.2. 
The product of the percentage of nitrogen and its molecular weight is 
80.7 X28 =2,259.6. The sum of the several products is 523.6+8.4+227.2 
+2,259.6 =3,018.8. Then, 


PER CENT. 
Carbon dioxide, by weight = 523.6+3,018.8=.17345—= 17.345 
Carbon monoxide, by weight = 8.4+3,018.8=.00278+ = .278 
Oxygen, by weight = 227.2+3,018.8=.07526+ = 7.526 
Nitrogen, by weight = 2,259.6 +3,018.8=.74851— = 74.851 
100.000 


Ans. 


22 FURNACE EFFICIENCY § 25 


SAMPLING 


31. Flue-gas analyses are made of boiler furnaces and daily 
records are kept, in order to learn the exact conditions that 
exist in any given power plant; no reliance whatever should be 
placed on guesswork methods. After the conditions are known, 
steps can be taken to secure greater economy, efficiency, and 
capacity. 

With perfect combustion of the fuel, the carbon dioxide, COs, 
formed is, in round numbers, 21 per cent. of the gases flowing 
into the chimney, the remainder being nitrogen, N, which comes 
in with the air supplied. 

With imperfect combustion the flue gases contain, in addition 
to carbon dioxide, CO:, and nitrogen, N, more or less carbon 
monoxide, CO, which is carbon incompletely burned, and 
usually some oxygen, O. It requires air for the combustion 
of fuel, but either too much or too little will cause a loss of 
heat. As the gases from a boiler furnace cannot be seen, it is 
impossible to know their composition without making an 
analysis. 


32. Samples of the gases to be analyzed are drawn from the | 


desired place through a sampling tube of platinum, porcelain, 
glass, or of metal cooled by water, care being taken to make 
an air-tight joint between the sampling tube and the opening 


\ 








Fic. 3 


into which it is inserted, using asbestos, plaster of Paris, putty, 
wet cotton waste, or other suitable material for this purpose. 
Care must also be taken to stop up all crevices in the boiler 
setting or flue through which air might leak and thus affect the 
composition of the gases to be analyzed. 


ay 


§ 25 AND FLUE-GAS ANALYSIS 23 


Fig. 3 shows a form of water-cooled, metal, gas-sampling tube 
consisting of an outer brass tube a surrounding a tube b 
through which is run the inner gas-collecting tube c. 
The tube a is about 3 feet long and 14 inches out- 


side diameter; the inner tubes } ’ 
C7. SSVI NS 
Will = 


and c Have diameters of $ and 4 

inch, respectively. The joint at — Pani oe 
the end d should be brazed, the la ercrar 
others being soldered. Water 

enters the tube 6 through the pipe e and flows toward 
the end d, into the outer tube a, thence out through 
the pipe f. 
























——— NW 


33. The gases to be analyzed are usually drawn 
from the combustion chamber, chimney, or flue by 
means of some kind of water or steam-jet aspirat- 
ing pump, one type of which is shown in Fig. 4. 
This pump somewhat resembles a boiler injector, 
its action in drawing the gases into the sampling apparatus 
depending on a flow of water from the pipe a through the con- 


aduug eacte spasussncsatecataseqiewsavcessdavestoTedic 


Fic. 4 





Soe <—_. stricted passage b into the 
oAspirator || waste tube c. As the water 
f “ passes by the orifice d of the in- 


Spiration tube e the pressure in 
the latter is reduced and the air 
or gas therein flows toward the 
orifice d, through which the gas 
is sucked by the water, mingling 
with it and passing to waste 
through the tube c. The collect- 
ing bottle is placed between the 
aspirator, or pump, and the 
sampling tube. A light check- 
valve f serves to prevent the 
Z entrance of air when the gas is 

Fic. 5 being drawn into the collecting 
bottle, or in case of stoppage of the water supply; the latter 
may be taken from any convenient source. 





24 FURNACE EFFICIENCY § 25 


34. In order to secure samples that may safely be taken 
as approximately indicative of the general character of com- 
bustion, it is advisable to use a quart collecting bottle of the 
kind shown in Fig. 5, in which the coilection of gas may go on 
continuously for $ hour or longer. Through the stopper of 
the bottle are inserted a short piece of glass tubing a and a 
siphoning tube b. The gas sampling tube, Fig. 3, the aspirator, 
Fig. 4. and the collecting bottle are connected by means of the 
glass Tc, Fig. 5, and short rubber-tubing connectors. When 
the bottle is connected as shown, the pinch cock f and screw 
cock on d are closed and the gas simply passes through the T ¢ 
from the sampling tube to the aspirator. Before collecting 
the sample, the air is expelled from the collecting bottle and 
the T by filling them with water. To fill the bottle with gas, 
the pinch cock and screw cock are opened slightly, and the water 
is slowly siphoned from the bottie through the tubes b and d 
while the gas is being drawn into the bottle. The water flowing 
from the collecting bottle is thus replaced by the gases of com- 
bustion. The flow of water from the collecting bottle through 
the siphoning tube b, and consequently the rate at which the 
sample of gas is collected, may be regulated by means of the 
screw cock on the rubber tube d, so as to secure an average 
sample for any desired length of time. Preferably, the water 
used in the collecting bottle should first be saturated with the 
gas to be examined in order to reduce the possibilities of error 
in making analyses. | 


ORSAT APPARATUS 


35. Among the several types of appliances for analyzing 
the gases of combustion, that shown in Fig. 6 and known as 
the Orsat apparatus is one of the most popwar. It gen- 
erally consists cf a burzite a, which 1s simply a graduated glass 
tube for measuring the gas confined in it, connected to three 
or more glass U-shaped tubes, or pzpettes, h, 7, and 7 containing 
chemical solutions for absorbing the different gaseous products 
of combustion, and a leveling bottle m for causing the gases to 
flow back and forth between the burette and pipettes. When 
the leveling bottle is raised, the water in it flows into the 


§ 25 AND FLUE-GAS ANALYSIS 25 


burette and causes the gas to pass into one of the pipettes. 
When the leveling bottle is lowered, the water in the burette 
runs back into the bottle, drawing the gas from the pipette 
back into the burette. To obviate errors due to temperature 
fluctuations that would otherwise affect the density of the gas, 
and hence the readings of the burette, the latter is enclosed, as 
shown, by a stoppered 
glass tube or jacket 
filled with water. 


36. The burette 
is connected to a thick 
tube g, Fig. 6, fas- 
tened in a cut bin the 
dividing panel and by 
means of a small brace 
c attached to the cover 
of the case. ‘The tube 
gq bends down at its 
farther end and con- 
nects with a U tube d 
containing loose cot- 
ton in the arms, to 
catch dust, and water 
in the bend, the pur- 
pose of the water being 
to saturate the gas: 
with moisture before 
measuring takes place. 
For increasing the ab- 
sorbing surface of the 
pipettes, they are filled 
with glass tubes, as shown. Each glass tube in 7 contains a 
spiral of copper wire. The rear ends of the absorption pipettes 
are closed by rubber stoppers containing small glass tubes that 
are connected to a rubber ball o of about 200 cubic centimeters 
capacity, the purpose of the rubber being to effectively exclude 
air and prevent oxidation of the liquids. As 1 cubic inch 







































































26 FURNACE EFFICIENCY § 25 


= 16.3872 cubic centimeters and 1 cubic centimeter = .061 cubic 
inch, the rubber ball o contains 200.061 =12.2 cubic inches. 


387. In the boiler room, it is advisable to substitute rubber 
connections and pinch cocks for the glass stop-cocks in k, Fig. 6, 
which, being fragile, are suitable for use in laboratory practice 
only. These stop-cocks are provided for controlling the flow 
of gas into the pipettes. At , where connection with the 
sampling tube or collecting bottle is made, it is advisable to 
provide a short rubber-tube connector that may be closed by 
a pinch cock. Piping connections between the Orsat and the 
sampling tube or the collecting bottle should be of tin, short 
pieces of rubber tubing being used to make joints. 

In charging the pipettes, the front legs are opened to the 
atmosphere, the stoppers and tubes are removed, and the 
chemical solutions are poured in until each pipette is about 
one-half full. In order that the solutions may be transferred 
from the rear legs of the pipettes to the front legs, where absorp- 
tion of the various gases takes place, the three-way cock ¢ is 
turned so as to establish communication with the atmosphere; 
then the burette is filled with water from the leveling bottle. 
The three-way cock e is now closed, the stop-cock in the tube 
to the pipette h is opened, the leveling bottle m is lowered, and 
as the water from the burette runs into the bottle the solution 
rises in the pipette h, and when it reaches the mark on the pipe 
k the stop-cock is closed. The reagents in the other pipettes 
are raised to the marks on the pipes k in the same way. The 
stoppers are then replaced and the tubes J are connected to the 
rubber bag 0. No air can leak by the rubber-tube connectors 
between the tube g and the pipettes, because the marks on the 
pipes k are above the connection, which is always moistened, 
and thus sealed by the solution in the pipette. 


38. The apparatus now being ready for manipulation and 
the required sample of gas having been collected, the pinch 
cock f of the collecting bottle, Fig. 5, is closed, and the bottle 
is disconnected from the aspirator and sampling tube and con- 
nected with the Orsat at ». The burette having been filled 
with water, the air in the connecting tubes of the Orsat is then 


§ 25 AND FLUE-GAS ANALYSIS 27 


exhausted by means of a rubber suction bulb g attached by 
tubing to the three-way cock e; otherwise, after drawing the 
first sample from the collecting bottle into the burette, instead 
of pure gas there would be in the burette a mixture of air and 
gas that would have to be thrown away, and another sample 
would have to be drawn in order to obtain pure gas. 

The air in the tubing connections between the collecting 
bottle and the pipettes and burette having been exhausted, 
the pinch cock f, Fig. 5, is opened and the three-way cock e, 
Fig. 6, is turned so as to establish communication between 
the burette and collecting bottle, from which gas is then drawn 
into the burette by lowering the leveling bottle m far enough 
to permit the water in the burette to run back into the bottle. 
Since the end of the tube d, Fig. 5, is immersed in the water 
siphoned from the collecting bottle, the gas withdrawn there- 
from is replaced by the water that flows back into the collecting 
bottle under the influence of atmospheric pressure. After 
allowing the burette to drain for a couple of minutes, the cock e 
is closed and the leveling bottle is elevated until the water in 
the burette rises to the zero mark, whereupon the pinch cock 
on the tube n, Fig. 6, is closed and the three-way cock e is 
momentarily opened to relieve the gas in the burette of any 
pressure greater than that of the atmosphere, communication 
with which is then cut off by closing the cock e. The level 
of the water jn the bottle m should then be brought to the same 
level as the water in the burette, namely, to zero, and the 
pinch cock on the tube ” opened. No readings of the burette 
should at any time be taken until after the water level in the 
burette and the bottle are brought to the same height. 

Having filled the burette with a good sample of gas, com- 
munication with the pipette h, containing a solution of caustic 
potash, KOH, for absorbing carbon dioxide, COz, is established 
by opening the cock, and the gas is forced from the burette 
into the pipette h by raising the leveling bottle m, so that the 
water therein will flow into the burette. By raising and lower- 
ing the leveling bottle, the gas is forced in and out of the pipette 
several times, the gas finally being drawn into the burette and the 
reading taken after the water levels in the burette and leveling 


[5] 


28 FURNACE EFFICIENCY § 25 


bottle are brought to the same height. The first reading should 
be checked by a second, or even by a third or fourth reading, 
if necessary. The decrease of volume due to the absorption 
of carbon dioxide by the solution of caustic potash shows what 
percentage of the sample consists of carbon dioxide. 


39. Having determined the amount of carbon dioxide 
present in a given volume of the gas, the gas in the burette 
is next forced into the pipette 7 that contains an alkaline solu- 
tion of pyrogallate of potash for the absorption of oxygen. 
Any loss of volume that may appear after passing the gas into 
and out of the pipette z at least eight times will represent the 
volume of oxygen in the given volume of gas. 


40. Finally, the gas is forced several times into and out 
of the pipette 7 containing an acid solution of cuprous chloride, 
CuCl, for the absorption of carbon monoxide, CO; when all 
the latter has been absorbed, that is, when the burette volume 
readings of successive trials agree exactly, no further diminution 
of volume being possible, the difference between the final 
reading and that obtained after passing the gas into the second 
pipette represents the volume of carbon monoxide present. 


41. After passing through the absorption process, the gas 
contains hydrogen, nitrogen, and compounds of hydrogen and 
carbon, or hydrocarbons, such as marsh gas, or methane, CH, 
the determination of the percentages of which is attended with 
too much difficulty to warrant an attempt at separation in the 
boiler room. Moreover, such determination is unnecessary, as 
the principal object of making flue-gas analyses is to ascertain 
whether or not combustion is complete, in order that the engi- 
neer may know whether or not the fires are properly managed 
and what changes should be made to secure greater economy. 

While using the apparatus, care should be taken to prevent 
drawing any of the solutions into the burette, and the latter 
should be permitted to drain thoroughly before readings are 
taken. A record should be kept to show the amount of gas 
absorbed by each of the solutions, in order that they may be 
renewed before they become saturated. A temperature change 
of 2°F. at the burette will affect its readings about .3 per cent. 


§ 25 AND FLUE-GAS ANALYSIS 29 


42. The caustic-potash solution is prepared by dissolving 
500 grams of potassium hydrate, KOH, in 1,000 grams of water. 
As 1 gram=.035 ounce avoirdupois and 1 ounce avoirdupois 
= 28.3495 grams, 500 X .035 = 17.50 ounces avoirdupois, closely. 

The pyrogallate-of-potash solution is made by dissolving 
120 grams of potassium hydrate, KOH, in 100 grams of water 
and pouring the solution over 5 grams of solid pyrogallic acid, 
which is thereby dissolved and absorbed. 

The cuprous-chloride, CuCl, solution is prepared by covering 
the bottom of a 2-quart bottle with copper oxide (scale) to a 
depth of about 3 inch and putting in the bottle a bundle of 
No. 12 gauge copper wire long enough to reach from top to bot- 
tom of the hydrochloric acid, HCL, which is next poured into 
the bottle. The bottle should be shaken occasionally during a 
period of 96 hours to insure a good solution, a fresh supply of 
hydrochloric acid, which should have a specific gravity of 1.10, 
being introduced whenever part of the solution is drawn off 
for use in the Orsat. Care should also be taken to renew the 
supply of copper oxide and wire whenever necessary, in order 
to insure a saturated solution. 


43. The reagents named possess absorptive powers approx- 
imately as follows: Caustic potash absorbs about 40 cubic 
centimeters of carbon dioxide, CO2, per cubic centimeter; 
pyrogallate of potash about 22 cubic centimeters of oxygen, O, 
per cubic centimeter; cuprous chloride about 6 cubic centi- 
meters of carbon monoxide, CO, per cubic centimeter. These 
proportions may vary, however, according to the strength and 
purity of the several solutions. 


44. As the pyrogallate of potash will absorb carbon diox- 
ide, COs, as readily as oxygen, O, the dioxide, COs, separation 
must be made first through the caustic-potash solution. Sim- 
ilarly, the cuprous-chloride solution will absorb both the dioxide, 
CO2, and oxygen, O, as well as carbon monoxide, CO; therefore 
this reagent must be used last to obtain the carbon monoxide 
in the sample of gas. 


45. If 100 cubic centimeters of a sample of gas are taken 
and of this 100 cubic centimeters, 12 cubic centimeters are 
ILT 168—4 


30 FURNACE EFFICIENCY § 25 


absorbed in the first pipette, the result indicates 12 per cent. of 
carbon dioxide, CO,. If, after analyzing to obtain the oxygen 
present, 18 cubic centimeters have been absorbed, then 18—12 
=6 cubic centimeters, or 6 per cent., of oxygen is present. 
Finally, if the total volume absorbed is 18.4 cubic centimeters, 
18.4—18=.4 per cent. carbon monoxide, CO, is present. 


HAYS GAS-ANALYSIS INSTRUMENT 


46. One of the small portable instruments used for making 
analyses of boiler-furnace gases is shown in Fig. 7, and is known 








ic, 7. | 


as the Hays gas analyzer. The working parts are protected 
bv a metal case having hinged doors front and back which are 


» 


§ 25 AND FLUE-GAS ANALYSIS 31 


opened to admit plenty of light when the instrument is in use. 
It may be suspended from a nail driven into the brick wall; 
conveniently near a in Fig. 8. The hand operated bulb a, 
Fig. 7, has a long rubber tube that is attached to a 4-foot length 
of 1-inch gas pipe, which is inserted into the gas flue of the boiler 
somewhere near a, Fig.8. By means of the bulb a, Fig. 7, the gas 
sample is pumped into the tall glass tube b. The leveling 
bottle c is filled with water and connected to the lower end of the 
tube b bya rubber tube. After closing the cock d towhich thegas 
supply tube from the bulb a is attached, the bottle c is lifted 
from the case and raised until the water level stands at the 















































—— 


— 


CLAM MUU 
GMaves GLEE 

ASSESS AT, 

PLA LLN 


CLL 





SILTEENTSD, 


Fic. 8 


zero mark on b. When the water in b and c stands at the same 
level, the gas sample in b is measured at atmospheric pressure. 

The stop-cock f is opened and the bottle c raised until the 
water level rises to the top of b, thus forcing the measured flue- 
gas sample through the potash solution in the tube e, where the 
carbon dioxide, COs, is absorbed. The bottle c is then lowered, 
allowing the water level to lower in 6 and the unabsorbed gas 
in e to flow back into b. The cock f is closed when the potash 
solution rises to the proper height in the tube e, and the leveling 
bottle c is held at such a height that the water level in b and c 
are at the same height. . 


32 FURNACE EFFICIENCY § 25 


The gas in the tube } will then be measured at atmospheric 
pressure as before, and the reading of the scale.on 6 will give the 
percentage of carbon dioxide, CO:,in the sample. With this 
apparatus the testing of a sample requires but a few moments. 


A. Table I gives the percentages of fuel losses, air excesses, 
and preventable losses for the different percentages of carbon 
dioxide, CO2, in the furnace gases. 

















TABLE I 
FUEL LOSS 
Pes Cect of At Excess Eo Fig) 1 eel aa 
Gases Per Cent. Pep Cents Per Cent. 
15 38.0 12 Oo 
14 47.8 13 I 
13 59.2 14 2 
12 72.5 15 2 
II 88.1 16 4 
10 107.0 18 6 
9 130.0 20 8 
8 158.7 23 II 
is 195-7 26 14 
6 245.0 30 18 
5 314.0 36 24 
4 417-0 40 30 
3 590.0 60 48 
2 935-0 go ee 
I 1,970.0 


——————— 











Theoretically, the highest attainable percentage of carbon 
dioxide, COz, is 20.9, which means that just sufficient air must 
be supplied to furnish the oxygen for perfect combustion. In 
practice, it is not possible to reach 20.9 per cent. of dioxide, COz, 
because it is necessary to have 88 per cent. excess of air to meet 
various conditions. With this amount of excess air, 15 per cent. 
of dioxide, COz, may be obtained, which is considered excellent. 


§ 25 AND FLUE-GAS ANALYSIS: O38 


The percentage of dioxide, COs, is an index of excess air.. The 
higher the percentage of CO, and the lower the temperature of 
the flue gases, the lower will be the percentage of loss. 

The values given in Table I are approximate only, and they 
are based on the assumption that the fuel is pure carbon. 
They are sufficiently close, however, for practical use, and for | 
making comparisons. The per cent. of fuel loss given in the 
third column of the table is found as follows: It takes 
11.6 pounds of air to burn 1 pound of carbon. By adding 38 per 
cent. excess air, 11.6X.388+11.6=16.008 pounds of air are 
required to burn 1 pound of carbon to carbon dioxide, CO2; 
for all practical purposes this may be taken as 16 pounds. 
This air is heated from an average temperature of 60° F. to 
about 500° F., therefore each pound of air is raised through 
500—60=440° F.; as the specific heat of air is .24, 44016 
xX .24=1,689.60 B. T. U. are required. As 1 pound of carbon 
contains 14,600 B. T. U., 1,689.6+ 14,600 = .116=11.6 per cent. 
loss. In Table I it is given as an even 12 per cent. loss to 
avoid the use of decimals. This 12 per cent. loss is considered 
non-preventable. 


DEFECTS REVEALED BY FLUE-GAS ANALYSIS 


48. Inone power plant, a flue-gas test showed the presence of 
6 per cent. of carbon dioxide. Table I shows that with 6 per cent. 
of dioxide in the flue gases, thereisa preventable loss of 18 percent. 
of the fuel thrown in the furnace. ‘Table I also shows that there 
was 245 per cent. excess air going through the furnace, which 
excess indicates the cause of the low percentage of dioxide. 

A sample taken a few moments later showed 9 per cent. of 
dioxide. The increase of 3 per cent. is due to the coal last 
fired having become incandescent. A third sample showed 
4.5 per cent. of dioxide, and a fourth sample showed 8 per cent. 
of dioxide. < 

The tests were continued for a period of 30 minutes with the 
results plotted from a to b on the chart, Fig. 9; the average 
dioxide is 6.2+ per cent. According to the table, this means a 
preventable loss of fuel of approximately 16 per cent. and an 
excess of air of 245 per cent., approximately. 


34 FURNACE EFFICIENCY § 25 


‘49, An inspection of the furnace under test revealed the 
following facts: The fire was about 6 inches thick. There 
were several large holes in the fire-bed at the back end of the 
grate. The whole surface of the fire was very irregular and 
uneven, and riddled with small holes by the strong blast from 
the steam blower in the ash-pits. The furnace doors were 
warped and open about $ inch around the top and sides, and 
air leaks were found at other places in the setting. ‘This large 


| fe fo [abjonda Jen Osi 2 xp 
Ps Pop op pedaeh, <i posi AT Sisal XA is 
LP Nas 
eS Se ee 
ee 


14 









CO, Percentages 
mn Oty Sa © 


23a e See 


4 30 36 42 48 54 60 
Minutes ; 
Fic. 9 


excess of air cooled off the furnace and carried considerable 
of the heat to the chimney, a waste that had been going on 
undiscovered for quite a while. 


50. A series of tests were made after the fires had been 
put in proper condition and the intensity of the draft reduced 
from .3 inch to .1 inch. The percentages of carbon dioxide 
from this series are plotted on the chart from c to d, Fig. 9, 
and show an average of 10.5 per cent. This means that by 
careful firing and intelligent management the preventable loss 
was reduced from 16 per cent. to 5 per cent. in round numbers, 
and the excess air reduced nearly 145 per cent. . 


" 


§ 25 AND FLUE-GAS ANALYSIS 35 


By stopping the leakage of air around the warped furnace 
doors and openings in the settings, 15 per cent. of dioxide could 
be obtained, although this is considered very high in practice. 


51. Two boilers were in service at the time of the test, the 
grate surface of each being 32 square feet. Three tons, or 
6,000 pounds, of coal were fired in 24 hours, an average of 
250 pounds per hour, and approximately 8 pounds per square 
foot of grate surface per hour for each boiler. The coal used 
was No. 3 buckwheat or washery culm that cost $1.15 a ton 
delivered. It contained 7 per cent. of moisture. 

The tests with the gas analyzer showed there was a prevent- 
able loss of fuel of 16 per cent. due to the manner of operation, 
under the conditions that existed at the time the tests were 
made. This loss amounted to 6,000.16=960 pounds of 
coal, or, so00 X $1.15 =$.55, or 55 cents a day, or $200, closely, 
a year of 365 days. As two boilers were in service, the amount 
that was needlessly lost is 2 $200 = $400 a year. 

In connection with this, there was the expense of handling 
the excess coal and ashes, which must be included in the regular 
expense account of the plant’s operation. Only by the use of 
a gas analyzer could the waste have been discovered. 

It is of the greatest importance that a draft only strong 
enough to burn the grade of fuel used, and keep the pressure 
of steam uniform, be employed. If high draft pressure is 
demanded, the fires must be thicker than is required with less 
draft. In no case should the draft be allowed to blow holes 
through the fuel bed. 


HEAT BALANCE 


HEAT-BALANCE DATA SHEET 


52. The heat balance is obtained by analyzing the data 
obtained during a boiler test; the data entering into the analysis 
are usually recorded on a heat-balance data sheet of the form 
here given. The values recorded here are fictitious, and are 
given in order that it may be shown how a heat-balance analy- 
sis is obtained from values recorded during a boiler test. 


we) 
or) 


OG yee ot ee 02 ae 


FURNACE EFFICIENCY § 25 


HEAT-BALANCE DATA SHEET 


Steam pressure, pounds per square inch, gauge (dry steam).. 190 
Temperature of feedwater, degrees F...... 0.0 eda scene 200 
Temperature of boiler room, degrees F.............2-ss0000 80 
Temperature of gases, at outlet, degrees F................. 478 
Weight of coal consumed per hour, pounds................. 5,700 
Moisture.in coal, per: cents, : Ue pelt rae '> beeeacs no 2.00 
Dry;coal pounds per hotur.. tite vip ee . tle wel. ne 5,586 
Ashes, pounds per DOUBs 3 gan. wap cis pusigatcs storu tas fee ae 550 
Ash-per cent."OF Ury COdie:. ge... ty oe a oe 9.84 
Actual evaporation, pounds per hour....................6- 57,000 
Carbon in the coal, per cent. 78.52 
Hydrogen in the coal, per cent. 5.46 
Oxygen in the coal, per cent. Ultimate analysis of dry 7.00 
Nitrogen in the coal, per cent. COAL. oc. ® cole se ile 1.21 
Ash in the coal, per cent. 6.5) 
Sulphur in the coal, per cent. 1.30 
Heat value of dry coal, British thermal units, per pound, as 
determined. by..a.calorimeter is... cre oak - « ae ae 14,230 
Heat value of combustible, British thermal units, per pound, 
as determined by calculation, involving items 9 and 17... 15,783 
Combustible, per cent., in the ash, by analysis............. 18.00 
CO per Centon VION. I, TEE Lk 14.35 
CO percent IT fPtse-s analysis "9 
JV. OT) CO be Liban aolageuo de re: Saal ane eee 81.03 


COMPUTATIONS PERTAINING TO HEAT BALANCE 


53. One pound of carbon completely burned to carbon 


dioxide, COs, gives out by its combustion 14,600 B. T. U., 
approximately. One pound of hydrogen when burned to 
form water gives out 62,000 B. T. U., approximately. From 
this data the following formula has been derived: 


A = 14,600 C+62,000(# 5) 


in which A=heat of combustion, in B. T. U.; 


C=percentage of carbon in fuel; 
H =percentage of hydrogen in fuel; 
O=percentage of oxygen in fuel. 


The small amount of sulphur that may be in coal is neglected 
in the calculations for heat value. It will be noticed that one- 


§ 25 AND FLUE-GAS ANALYSIS 37 


eighth of the percentage of oxygen is subtracted from the per- 
centage of hydrogen before multiplying by the heat value of 
the hydrogen. This is done because the oxygen in the fuel 
combines with one-eighth of its weight of hydrogen and so 
renders this amount of the hydrogen unavailable for combus- 


tion, so that only the remainder may be considered, or H -< 


By the use of the formula, the heating value of a coal may be 
determined sufficiently accurate for all practical purposes, and 
serve as a guide as to what may be expected of a given coal 
when fed to the furnace of a steam boiler. 

EXAMPLE.—A bituminous coal has the following composition: Carbon, 
76 per cent.; hydrogen, 6 per cent.; oxygen, 12 per cent.; nitrogen, 1 per 
cent.; sulphur and ash, 5 per cent. Find the heat of combustion. 


SOLUTION.—Applying the formula, 


12 
A = 14,600 X .76+-62,000 x (.00-%) =13,886 B. T. U. Ans. 


54. When finding the heating value of a coal there will be 
a slight difference in the final result according to whether an’ 
ultimate or a proximate analysis of the fuel has been made. 
The difference is rather slight, however. The formula just 
given is that used in an ultimate analysis, and if this formula 
is applied to the data given on the heat-balance data sheet, 
already shown, it will be found that a heat value of 14,306+ 
B. T. U: is obtained, instead of the value of 14,230 B. T. U. 
given, which is the result of a proximate analysis. The differ- 
ence is so slight as to be of no practical account; consequently, in 
practice the heating value obtained by whatever analysis is 
most convenient will be used in heat-balance calculations. 


55. The factor of evaporation is found from the following 
formula: 
_H-h+32 
966.1 


in which f=factor of evaporation; 
H=total heat of steam at observed pressure; 
h=temperature of feedwater entering boiler. 


I 


38 FURNACE EFFICIENCY § 25 


The actual evaporation multiplied by the factor of evapora- 
tion gives the equivalent evay oration from and at 212° F. 


EXAMPLE.—From the data recorded on the heat-balance data sheet in 
Art. 52, determine the equivalent evaporation per pound of coal, the 
B. T. U. of heat utilized, and the efficiency of the boiler, furnace, and grate, 


SOLUTION.—From the Steam Tables, the total heat of steam at 190 lb. 
gauge pressure is 1,198.93 B. T. U. Applying the formula, 
_ 1,198.93 —200+32 
ue 966.1 | 
Then, equivalent evaporation is 57,000 X 1.067 =60,819 lb., and equiva- 
lent evaporation per pound of dry coal fired is 60,819+5,586=10.89 Ib., 
nearly. Ans. 
The heat utilized by the boiler is 10.89 966.1 =10,520.8 B. T. U. per 
Ib. of dry coal. Ans. 
The efficiency of the boiler, furnace, and grate, by Art. 2, is 10,520.8 
+ 14,230 =.739 =73.9+ per cent. Ans. 


= 1.067+ 


96. The formula by which the loss due to moisture in the 
coal is computed was given in Art. 7. An application of the 
formula to the balance sheet under consideration is given in 
the following example. 


EXAMPLE.—From the data given on the heat-balance data sheet, deter- 
mine the heat loss per pound of coal due to moisture in the coal, and also 
the heat loss in per cent. 

SOLUTION.—Applying the formula given in Art. 7, 

A =.02X[(212—80) +966.1-+-.48 x (478 — 212)] = 24.52 B. T. U. 


Percentage of heat loss is 24.52+14,230=.0017 =.17, say .2, per cent. 
Ans. 


57. The formula for calculating the heat loss due to burn- 
ing of the hydrogen was given in Art. 8. The application to 
the balance sheet under consideration is given in the following 
example. 


EXAMPLE.—From the data given on the heat-balance data sheet, deter- 
mine the heat loss per pound of coal due to the burning of the hydrogen 
in the fuel, and also the heat loss in per cent. 


SOLUTION.—Applying the formula in Art. 8, 


A=9X.0546 X [(212 —80) +966.1+.48 x (478 —212)] 
= 602.35 B. T. U. per lb. 


The heat loss is 602.35 + 14,230 = .0423+ =4.23+ per cent. Ans. 


§ 25 AND FLUE-GAS ANALYSIS 39 


58. To compute the loss in the heat taken away by the 
dry chimney gases per pound of coal, the weight of such gases 
must first be found by formula 1, Art. 9, and then the heat 
loss is calculated by formula 2. 


EXxAmMPLE.—From the data given on the heat-balance data sheet in 
Art. 52, determine the percentage of loss of heat by the escaping chimney 
gases, per pound of dry coal, and also in per cent. 


SOLUTION,—Applying formula 1, Art. 9, and remembering that the 
quotient is to be multiplied by the percentage of carbon in the coal, 
w= 11X.14385+8 X .045+7 X (.0012+-.8103) 


3X (.1485+.0012) 
=13.78+ Ib. per lb. of dry coal 


Applying formula 2, 
A =.24X13.78 X (478—80) =1,316 B. T. U. per Ib. of dry coal 


Hence, heat loss in per cent. =1,316+14,230=.093=9.3 per cent., 
closely. Ans. 


X .7852 


59. The heat loss due to incomplete. combustion is ccm- 
puted from the percentage of carbon monoxide shown by a 
flue-gas analysis, using the formula presented in Art. 11. 


EXAMPLE.—From the data given on the heat-balance data sheet pre- 
sented in Art. 52, find the heat loss, in per cent., by incomplete com- 
bustion of the coal. F 

SOLUTION.—Applying the formula in Art. 11, 

10,150 X .0012 
A =.7852X ——_———— = 66.09+ B. T. U. lb. of d ] 
"1435 -+.0012 vs Bia lis OB adh st 


Percentage of heat loss is 66.09+ 14,230 = .0046 =.46, say .5, per cent. 
Ans. 


60. The manner in which the heat loss due to unconsumed 
carbon in the ash is found has been explained in Art. 12. 
EXAMPLE.—From the data given on the heat-balance data sheet in 


Art. 52, determine the percentage of heat loss due to unconsumed carbon 
in the ash. 


SOLUTION.—By Art. 12, the heat loss per pound of dry coal is .0984 
X<.18 x 14,600 = 258.6 B. T. U. and the percentage of loss is 258.6 + 14,230 
=.0181=1.81 per cent. Ans. 


61. The manner in which the unaccounted for losses are 
found was stated in Art. 17. Applying this article to the data 


4() FURNACE EFFICIENCY § 25 


of the heat-balance data sheet, the heat loss unaccounted for is 
found in B. T. U. and in per cent. as follows: By the method 
in Art. 4, the heat absorbed per pound of dry fuel is 10,520.8 
B. T. U., or 73.9 per cent. By Arts. 7 to 12, the accounted 
for heat losses per pound of dry coal are 24.52, 602.35, 1,316, 
66.09, and 258.4 B. T. U., or .15, 4.23, 9.3, .46, and 1.81 per 
cent. Hence, the unaccounted for heat loss per pound of dry 
coal is 14,230 — (10,520.8-++24.52+ 602.35 +1,316+ 66.09+258.4) 
= 1,441.84 B. T. U., and in per cent. 100—(73.9+.15+4.23 
+9.3+.46-+1.81) = 10.15, say 10.1, per cent. 


62. Afterall the various items of the heat balance have been 
calculated from the data obtained during a boiler test, they 
may conveniently be arranged in tabular form as here shown. 

HEAT-BALANCE TABLE 


B. avs | Per Cent. 
Values Values 





Items 


ee a 


1. Heat absorbed by the boilers, per pound dry 


COCLDRITL I Erneta 3). a's ow ss vbteee eee enol 10,520.80 73.9 
2. Loss due to evaporation of moisture in coal. . 24.52 2 
3. Loss due to moisture by burning of hydrogen. . 602.35 4.2 
4. Loss due to heat taken away in the dry chim- | 

TIGY SASESF ecca as « x’ sigiegh a's p coer kee Ghee eee 1,316.00 9.3 
5. Loss due to incomplete combustion.......... 66.09 5 
6. Loss due to combustible in the ash........... 258.40 1.8 
7. Loss due to radiation and unaccounted losses..| 1,441.84 10.1 


Totals (B. T. U. per pound of dry coal, 14,230) | 14,230.00 100.00 





A heat-balance scheme may be made more elaborate than here 
explained, but for practical power-plant purposes that which 
is given fulfils all reasonable requirements including that of 
simplicity. , 


APPLICATION OF HEAT BALANCE 


63. <A heat balance should be made in connection with 
any boiler trial, during which sufficient data, as given in Art. 62, 
has been obtained, in order to determine how the heat is 


§ 25 AND FLUE-GAS ANALYSIS 41 


distributed, and where losses occur. Steps may then be taken 
to correct irregularities and prevent further loss, or at least to 
reduce such losses to a minimum. 

In cases where complete and accurate data are not available, 
assumptions may be made and applied to the heat-balance 
scheme, and thus indications of unusual losses obtained. It 
is better to find the losses in this manner than not to attempt 
to do so owing to the absence of such data. 

It frequently happens that the greatest loss is that due to 
the chimney gases, which depends directly on the weight and 
temperature of the gases leaving the boiler. The lower limit 
of the weight of gas is fixed by the least amount of air required 
for complete combustion. When the supply of air is too small, 
the loss caused by burning the carbon to carbon monoxide 
instead of to carbon dioxide is more than the gain in decreasing 
the weight of gas. The lower limit of chimney temperature 
depends, to a great extent, on the temperature necessary to 
make sufficient draft for good combustion. This limit, with 
natural draft, is in the neighborhood of 400° F. 


TABLE II 
RELATIVE HEAT VALUES 





Percentage of Heat 
Distribution of Heat SET SERIE EEE 

















I 2 3 
1. Absorbed by boiler. . eee ROL SOC ers O 
2. Carried away by dry eae? be gases. .|°°24.0| 16.0] 10.0 
3. Radiation and unaccounted for hated T5077 W12.0" 1G-0 
4. Moisture formed by burning of hydro- 
Pe ate). . FUL OH PAOLO 4.0 3.5 3.0 
5. Evaporating moisture in coal........ 2.0 2.0 Wis 
6. Incomplete combustion of carbon....| 5.0 1.5 hr 
BPRaCeh EEG tee beer kee ae 100.0 | 100.0 | 100.0 











64. Table II, compiled by the United States Geological 
Survey, gives an approximate distribution of heat for Illinois 


42 FURNACE EFFICIENCY . |e 


bituminous coals, and shows the relation that exists between 
the various items. Column 1 gives the heat distribution when 
the conditions were poor; column 2 represents average con- 
ditions; and column 3, the best attainable in practice. These 
best conditions are seldom attained, but they are possible and 
will serve as an ideal to work for. 


65. The theoretical weight of air, at 62° F., required to 
burn 1 pound of the coal specified in the data sheet in Art. 52, 
is found from the following formula: 


W= 11.6¢4-84.8(17—2) 


in which W =weight of air, in pounds; 
C=percentage of carbon in coal; 
H = percentage of hydrogen in coal; 
O=percentage of oxygen in coal. 
EXAMPLE.—From the values given.in the heat-balance data sheet in 


Art. 52, determine the weight of air required theoretically to burn 1 pound 
of the coal specified. 


SoOLUTION.—Applying the formula, 


/ 


W =11.6X.7852+34.8 X (os10-—") =10.7 lb. Ans. 

The temperature of the air in the boiler room is given in the 
heat-balance data sheet in Art. 52 as 80° F., which is 48° above 
32°. The specific heat of air may be taken as .2375, so that 
each pound of air admitted to the furnace brings in 48 X .2375 
=11.4 B. T. U., and hence, since for each pound of the coal 
mentioned in the data sheet 10.7 pounds of air are theoretically 
required, as just calculated, the 10.7 pounds of air bring into 
the furnace 10.7 X11.4=121.98 B. T. U. 


ANALYSIS OF ASH 


66. True ash in coal is not combustible; it is the residue 
in the coal that will not consume by burning. It is the mineral 
matter in the coal as distinguished from the organic matter. 
An average analysis of ash from a number of anthracite and 
bituminous coal samples gave the following: 


§ 25 AND FLUE-GAS ANALYSIS 43 


Silica, from 50 to 60 per cent. 
Alumina, from 25 to 30 per cent. 


HO Th oa WEES 6) 2 eee patil fae ee WAG a oA gr weal ah 

PaO, no eer, wl, aAPE ELA WAL wll are eigialbly Less 
DS EC SUE eter sings dle tes pee Ry Sele CER EN 2. 9 IE than 
Beiicliew (POLASIL ANG SOUS). oo. kas a cue tas dees 5 per cent. 
SMARTER Meas heres) MAG eed g ce sie welt ecole 4 sie aed each 
RIGA U Sie atreiea aoa ce dene ae aiaaces 6 ce ¢nteceen ee A 


This analysis is given only for the purpose of reference. 
Analyses of coal and ash can only be made in laboratories 
equipped for the purpose, and by persons trained in that line 
of work. 


DRAFT AND DRAFT GAUGES 


MEASUREMENT OF CHIMNEY DRAFT 


67. With a given load on the boiler and a given kind and 
grade of fuel, there is a certain draft that will give the best: 
combustion. By draft is meant the pressure difference between 
the furnace and the chimney. The greater this difference, the 
larger will be the volume of gas passing over the heating surface 
and the more rapid will steam be generated. This is true, 
however, only when no more excess air is admitted to the 
furnace, either from below or above the grates, than is required. 
When the combustion is not producing the desired results, the 
carbon-dioxide readings will indicate what is the trouble and 
where to look for it. 

Draft may be expressed either in inches of water or in the 
weight of an equivalent column of water. A column of water 
12 inches high exerts at the base a pressure of .484 pound 
per square inch. As 1 pound avoirdupois contains 16 ounces, 
.434 pound contains .434 x 16 = 6.944 ounces; therefore, a 1-inch 
column of water will exert at its base one-twelfth of this pres- 
sure, or 6.944+12=.5786++ ounce per square inch. Therefore, 
when the gauge reading is known, the equivalent pressure in 
ounces may be found by multiplying the gauge reading by .5786. 


EXAMPLE.—In a certain boiler plant the draft is maintained at 1.5 inches 
of water by gauge. What is the equivalent pressure? 


FURNACE EFFICIENCY § 25 


44 


Ans. 


.8679 oz. per sq. in. 


1.5 X .5786 


SOLUTION.— 


68. 
the equivalent inches of water may be obtained by multiplying 


the pressure by 1.728. 


If the draft is expressed in ounces per square inch, 


EXAMPLE.—If the draft pressure is 1.1 ounces per square inch, what is' 


the corresponding height in inches of water? 


=1.9+ in. Ans. 


1.1X 1.728 


SOLUTION.— 


69. 
inches of water and pressure in ounces, in connection with 


The diagram in Fig. 10 shows the relation between 


1.163 oz. 


BRZS0UNSeRReD 
RATAN ARR 


F 
6 1. 


51 


. 





1 12 13 1.4] 


Ounces , Per Square Inch 


. 





ESh40 JRAiSS BSS EC RES p. 
SC SKUG OR TRRR SRR CRA 


BEES UONBL SIAR CES 
HS SRRNESEE SERVER Eee 8 
hone See eh 2 eS ee 
et Lt ae Tae TS fe ets Tela Te 


PT PT AS ee eae 
SNe sERRERERREORR 
SER, SARRBRRRRE MSRM 


| 
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|_| 
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a 
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Si 
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draft. 


The horizontal row of figures at the base represent 


The vertical row of 


figures at the left-hand side of the diagram represent the draft 


in inches of water, as measured by a draft gauge. 


ounces per square inch draft pressure. 


Knowing the draft in inches of water, in any given case, the 
corresponding pressure per square inch is found by locating the 


§ 25 AND+FLUE-GAS ANALYSIS 45 


point on the diagram from the indication of the draft gauge, 
and then running horizontally to the right to the intersection 
of the diagonal line, and down to the base where the corre- 
sponding pressure is found. 


EXAMPLE 1.—The draft, as measured by a water gauge, is linch. What 
is the corresponding pressure? 


SOLUTION.—Following the horizontal line representing the 1-inch draft 
to its intersection with the diagonal line and then following the nearest 
vertical line to the scale on the bottom shows that the corresponding pres- 
sure is .58 oz. per sq. in. Ans. 


EXAMPLE 2.—If the draft pressure is .9 ounce, what is the corresponding 
height of water in inches? 


SOLUTION.—Following the vertical line representing the pressure of 
.9 ounce to its intersection with the diagonal line and then following the 
nearest horizontal line to the scale on the left, it is found that the height 
of the water column is 1.5 in. Ans. 


NATURAL DRAFT 


70. The difference between the weight of a column of hot 
gases in a chimney and the weight of an equal column of cool 
air outside results in an upward motion of the hot gases in 
the chimney, which motion is termed natural draft. Any gas 
is lighter when heated than when it is cool, considering a given 
volume. ‘The force acting upwards is greater than that acting 
downwards, hence the phenomenon that is called draft. 

In any chimney, the higher the temperature, the greater the 
difference in pressure and velocity of flow of the gases; but, as 
the density of the gases decreases with the increase of temper- 
ature, there is a point where as much is lost in weight of gas 
passed, by the lightness of the gas, as is gained by the increased 
velocity. 


G1. The temperature of the gases in a chimney may vary, 
but under usual conditions of operation they will be from 
400° F. to 500° F. while the air outside the chimney may have 
a temperature of from 40° F. to 90°F. Asa result, the pressure 
in the chimney is less than the pressure of the air outside, so 

ILT 168—45 ; 


46 FURNACE EFFICIENCY § 25 


that air will flow through the furnace and up the chimney. 
As an example, assume that the temperature of the gases in 
a chimney 150 feet high and having a cross-section of 1 square 
foot is 500° F. As such a gas column weighs approximately 
4 pounds while at 60° F. the column weighs approximately 
114 pounds, the difference in pressure at the foot of the chimney 
of the gases inside and the air outside the chimney is 113 —63 
=5 pounds. This difference in pressure of the air inside and 
outside the chimney is known as the draft pressure. 


72. Since natural draft is dependent on the difference in 
weight between the hot gas in the chimney and the outside air, 
the hotter, and therefore the lighter, the gas, the stronger is 
the draft. A high chimney will cause a stronger draft than a 
short one; with chimneys of moderate height a strong natural 
draft requires a high temperature of escaping gases, with a 
consequent loss of heat and economy. With natural draft, the 
tate of combustion will range from 12-to 20 pounds of coal per 
square foot of grate surface per hour, depending on the quality 
of the coal and surrounding conditions. 


73. The capacity of a chimney varies as the square of the 
diameter and as the square root of the height. The velocity 
of flow of the gases, which is also a measure of volume, increases 
as the square root of the pressure, and the pressure varies 
directly as the height. 

By doubling the height of a chimney, the intensity, or, in 
other words, the pressure of draft, will also be doubled; but the 
velocity of flow of the gases will increase only as the square 
root of the pressure, which is the same as saying as the square 
root of the height. Ina chimney 200 feet high, the theoretical 
velocity of flow of gases will be twice that of a chimney 50 feet 
high, for the square root of 200 is 14.1421 and of 50 is 7.0711; 
therefore, twice as much gas will be discharged in a given time. 

In the foregoing, frictional resistances have not been con- 
sidered, but in practice these may be taken into account. The 
extent to which these resistances will affect the results, though, 
cannot be determined by any general law, for they will be 
greatly affected by the conditions of each case. 


§ 25 AND FLUE-GAS ANALYSIS 47 


74. The capacity of a chimney is not measured by the 
' intensity of draft. The capacity, for the same temperature, 
varies as the square root of the intensity, where the greater 
intensity is gained by an increase in chimney height. But if the 
temperature also is raised so as to double the volume of gas 
discharged, the intensity of the draft is doubled, and the 
velocity increased 1.414 times, but the velocity must be increased 
two times to pass twice the volume of gas in-the same period 
of time. ° 


75. Changes in draft should be made by manipulating the 
chimney damper and not the ash-pit doors. If the draft is 
varied by means of the ash-pit doors, while the regular damper 
remains wide open, the full draft of the chimney is exerted on 
the furnace all-the time. If the ash-pit doors are nearly closed 
the effect is to increase greatly the amount of air drawn into 
the furnace at all other points. The amount of air drawn in 
over the fire, as well as that getting in through cracks in the 
setting will be increased. 

On the other hand, if the damper is partly closed, with the 
ash-pit doors open, when less draft is required, there will be a 
drop in the draft at all parts of the setting, and, relatively, the 
amount of air drawn in both under and over the fire will be 
the same as before. 


76. Differences in pressure in boiler furnaces and chimneys 
are measured by draft gauges. They will not directly measure 
the flow and velocity of the gas, but the indications of the gauge 
will give an idea of the variation of velocity. 

When fires are clean and of uniform thickness, with the 
furnace doors closed and the ash-pit doors open, the greater 
the intensity of draft, the greater will be the velocity of flow 
of gases. If the ash-pit doors are closed, the draft, as indicated 
by the gauge, will be increased but the movement of the gases 
will be decreased, since the supply of air is shut off. If now the 
furnace doors are opened, air will rush into the furnace with 
considerable velocity but the gauge will show that there is less: 
draft; that is, less difference in pressure than before the furnace 
doors were opened. 


48 FURNACE EFFICIENCY § 25 


MECHANICAL DRAFT 


77. Mechanical, or artificial, draft is produced by means of 
steam jets or fan blowers. The object is to increase the differ- 
ence of pressure between the ash-pit and the chimney beyond 
that obtained with a chimney producing only natural draft, 
and at the same time to provide for a full supply of air to the 
grates as required by the rate of combustion desired. ; 


BALANCED DRAFT 


78. The term balanced draft is applied to a system of oper- 
ating boiler furnaces by which the supply of air and the rate of 
flow of waste gases from the chimney are so controlled that an 
approximately uniform atmospheric pressure is- maintained 
above the fire in the furnace for varying rates of combustion. 
By the use of this system, the air supplied to the fuel can be 
limited to the required amount for any desired rate of com- 
bustion. With it there will be neither an excess of pressure 
nor a partial vacuum in the furnace, thus differing from the 
natural and mechanical draft systems as usually applied. 


79. The draft is balanced by throttling the gases escaping 
to the chimney by varying the opening of the damper to 
suit the speed of the fan blower that supplies air to the asb-pits. 
The speed of the blower is governed by variations in steam 
pressure in the boiler. The position of the damper changes 
with change of speed of the blower, which in turn may be con- 
trolled by the steam pressure running the blower engine. 

The blower is so designed that it will deliver, approximately, 
a constant volume of air of variable pressure for any given 
speed. The volume varies with the speed, and the pressure 
varies with the resistance. The pressure in the ash-pit varies 
with the thickness of the fuel bed, and the volume of air varies 
with the demands for steam made on the boiler, with the result 
that only the least amount of air required for the necessary 
rate of combustion is furnished. 


80. The object of moving the damper in relation to the 
speed of the blower is to maintain atmospheric pressure in the 


§ 25 AND FLUE-GAS ANALYSIS 49 


furnace. The damper regulator is so adjusted that the damper 
is open just enough to accommodate the gases escaping from 
the furnace without creating a pressure therein, and without 
Opening so wide as to allow the chimney draft to produce a 
partial vacuum in the furnace. The chimney simply removes 
the gases from the furnace. The draft created by the chimney 
is throttled by the partly closed damper until the suction is 
sufficient to overcome the friction of the gases against the 
surfaces with which they come in contact. 


81. With balanced draft, the amount of hot gases is reduced 
to a minimum, and therefore they can take a longer time to 
pass through the furnace on the way to the chimney, and thus 
will give up a greater percentage of heat than would otherwise 
be the case. Although the furnace is kept at atmospheric 
pressure, the pressure falls slightly at the point where the gases 
leave the boiler, so that a partial vacuum exists in the passages 
leading to the chimney. This reduction of pressure is sufficient 
to overcome the frictional resistances of the passage of the 
gases, resulting in the gases being brought in contact with all 
the heating surfaces. When balanced draft is employed, leak- 
age of air through openings and cracks into the furnace will 
not so readily occur. 


82. The causes of low carbon-dioxide percentages are 
excess air, insufficient air, and improper mixture of air with 
the gases from the fuel. The causes of excess air are too strong 
a draft, too thin a fire-bed, holes in the fire, leaks in various 
parts of the boiler setting, doors, and chimney connections. 
The causes of insufficient air are insufficient draft, too thick a 
fire-bed, ashes on the grate, and too heavy a charge of fresh fuel. 


83. The remedies for these troubles are as follows: If the 
draft is too strong, it should be reduced or the thickness of the 
fire-bed increased. If the fires are too thin, the draft should 
be reduced or the thickness of the fire-bed increased. For 
insufficient draft, the thickness of the fire-bed should be 
decreased and the air spaces in the grates kept free and clear 
of slag. 


50 FURNACE EFFICIENCY § 25 


Leaks in the setting should be located by asing a lighted 
candle, as shown in Fig. 11. The leaks should then be plugged 

| with waste and asbestos 
Glebe mceelt mixed with a thin solution 
of fireclay and water. Air 
should not enter the fur- 
nace except through the 
means provided for that 
purpose and where it can 
be controlled. The tubes 
and flues should be cleaned 


rt ‘i M(t of soot and ashes, and holes 





Alas 
Z [| “Wy 
pieeneen ease. 


and the bed leveled, but 
they should not be filled with fresh fuel. 

If the covering of fresh fuel is too thick, a lighter cover should 
be given at next firing, and meanwhile air should be admitted 
above the fire-bed through the openings in the furnace doors. 
The combustion of the gases driven off the surface of the fire- 
bed will thus be assisted. 


DIRECT-READING DRAFT GAUGES 


84. The simplest form of draft gauge is that 
known as a direct-reading draft gauge, and 
is shown in Fig. 12. It consists of a bent U tube 
partly filled with water, and a scale located be- 
tween the inverted legs of the gauge. The ends 
are open at the top, and when the gauge is in 
use the ends are connected by tubing to the two 
places between which the difference of pressure is 
desired, as, for example, the ash-pit and the fur- 
nace above the fire; or, between the external air 
and the base of the chimney. With equal pres- 
sure in both places, the water will stand at the 
same height in both legs. With a difference of pressure, the 
water will rise in one leg and fall in the other, the movement 
of the water being toward the place of lesser pressure. 





Pigsae 


in the fire should be covered | 


§ 25 AND FLUE-GAS ANALYSIS 51 


The difference in pressure is then measured by tlie weight of 
a column of water equal to the difference in height between the 
two columns. In Fig. 12 the difference in the two water 
levels h and 2, represents the intensity of the draft and measures 
2 inches of water. 


85. With ordinary chimney draft, the pressure is usually 
from % to 2 inch; with light forced draft, it is from 4 to 1 inch; 
and with heavier forced draft, it is from 1 to 3 inches; in torpedo 
boats, the draft pressure may rise to a height of 6, or even 
7, inches. 


DIFFERENTIAL DRAFT GAUGES 


86. <A differential draft gauge is one by which smaller 
differences of pressure may be measured than is possible with 
the direct-reading draft gauge. The fluid in the measuring 
tube of a differential gauge moves a greater distance than that 
due to difference of pressure, as would be measured by a vertical 
column of the fluid. This is due to the angle of inclination, 
clearly shown in Fig. 13, given the measuring tube of that 





HG. 13 


instrument. For instance, if the inclination were one to five, 
the reading on the graduated scale would give five times the 
difference in water level between the vertical column and that 
in the inclined tube. Thus, minute differences in pressure are 
measurable. The gauge must be set level in order to give 
correct results; a spirit level attached to the frame of the gauge 
shows when this position is obtained. There are several 
makes of draft gauges on the market, but those illustrated and 


52 FURNACE EFFICIENCY § 25 


described show the principles involved and the manner of 
application and operation of such instruments. 


87. In Fig. 13 is shown the Hays differential draft 
gauge, which has two scales of measurement, the upper one 
reading in fractions of an inch, and the lower one reading in 
millimeters. Difference of pressure of roo inch may easily be 
determined on this gauge. Oil is used as the fluid instead of 
water, because its capillary attraction is constant, it is self- 
correcting, and it is not so volatile. To compensate for the 
difference in specific gravity, and indicate the equivalent head 
of water on the scale direct, comprising the fall in the indicating 
tube, and the rise in the oil chamber, the gauge is standardized ! 
for a corresponding higher oil head, necessitating no corrections. 

Mineral oil is used because it has little, if any, evaporation 
and it lubricates the surface so that a constant movement is 
attained. The oil may be colored red or blue. For permanent 
draft gauges, water is not as desirable as oil, as it has a variable 
capillary attraction on both wet and dry surfaces, of from 
.02 to .05 inch. Water may be, and is, used in temporary 
gauges, which are not permanently set up and connected. 

The construction of the gauge is shown in Fig. 14. The 
oil chamber a is drilled in metal and reamed to a uniform size 
throughout. The indicating tube b is rigidly cemented into 





Fic. 14 


the chamber a as shown, is yieldingly connected at the pressure 
end of the gauge c, and all stresses due to expansion and con- 
traction are taken up by the rubber d. 


88. The gauge may be connected as follows: Drill a hole 
in the front or side wall of the furnace large enough to admit 
a piece of 1-inch iron pipe. If the hole is drilled at the side, it 
should be as near the front end and top of the furnace chamber 
as possible, so as to avoid accumulations of slag and refuse 


825 AND FLUE-GAS ANALYSIS 53 


which would obstruct the end of the pipe. Cement a piece of 
l-inch pipe in the hole and cut it of such length as to extend 
half way through the firebrick lining of the furnace. Connect 
a T fitting on the outer end of the pipe and close the end opening 
with a plug. Connect the draft gauge to the side opening of 
the T with a 32-inch pipe in the usual manner. Should the 
l-inch pipe collect soot or ash dust, it may be cleaned by 
removing the plug at the end of the T. 


89. In connecting the gauge, care must be taken to set it 
true according to the indications of the spirit level inserted at 
the top of the gauge. Connection between the gauge cock and 
the #-inch pipe is made by the use of coiled tubing and coup- 
lings and the required bushings for the necessary reduction in 
the sizes of the piping. 

The plug at the upper end of the T at the right-hand side 
of the gauge is for the purpose of filling the chamber with the 
indicating oil, which must stand at zero on the scale when the 





Fic. 15 


instrument is ready for use. In order to test the accuracy of 
the gauge at any time, the stop-cock is turned so that the air 
vent in it will be open, when the oil should appear at zero. 
If for any reason it is not at the zero mark, the level may be 
corrected by adding or removing a quantity of oil. In refilling, 
the same kind of oil as the gauge was graduated with must be 
used. 


90. In Fig. 15 is shown the Ellison compound differ- 
ential draft gauge. This gauge multiplies the liquid move- 
ment ten times, indicating on one side of zero the furnace 
draft, and on the other side variations in the air supply; it 
gives a wide fluid travel under slight variation in furnace 


54 FURNACE EFFICIENCY § 25 


draft. The movable attached pointers shown are set for the 
most economical performance by gas-analysis determinations. 
The chamber end of the gauge is connected with the last pass, or 
with the breeching on the boiler side of the damper, and the 
indicating-tube end of the gauge is connected with the furnace. 
This combination differential draft gauge and differential 
air-supply gauge affords a great advantage in the economical 
operation of boiler furnaces. 

When both cocks are closed, both ends of the gauge are open 
to the atmosphere through the vents in the cocks for that pur- 
pose; then the fluid should stand at zero on the scale. The 
movable pointers are set to indicate an economical range of 
draft for a certain change in load and thickness of fuel bed. 


91. In Fig. 16 is shown the Ellison multiple differen- 
tial draft gauge, which is made up of two single gauges 














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Fic. 16 


mounted on one plate, and cross-connected with copper tubing. 
The upper gauge continuously indicates the furnace draft, and 
the lower gauge continuously indicates the variation in the air 
supply by the drop in pressure between the flue and the furnace. 
Both stop-cocks are vented so that the gauges may be open to 
the atmosphere and the levels of the liquids observed for 
accuracy. 

The pointers on both gauges are set for best conditions of 
economy as to air supply and draft pressure by gas-analysis 
determinations. 

As the gauges are independent of each other, the air-supply 
gauge is made with a longer scale than the furnace gauge, and © 


§ 25 AND FLUE-GAS ANALYSIS 55 


each scale has a different ratio, to suit different draft pressures 
and air-supply conditions. The scales of differential draft 
gauges may be made to magnify the movement of the vertical 
liquid column five, ten, or fifteen times. 


AUXILIARY APPARATUS 


MERCURIAL THERMOMETERS 


92. The ordinary types of mercurial thermometers are 
not suitable for measuring temperatures above 500° F., because, 





























BiG.) 17, 


_at atmospheric pressure, mercury boils at 676° F. For measur- 
ing higher temperatures, up to 1,000° F., mercurial thermometers 


56 FURNACE EFFICIENCY § 25 


are made with the space above the mercury filled with nitrogen 
gas; then as the mercury expands the gas is compressed, thereby 
increasing the pressure and raising the boiling point. 


93. In Fig. 17 is shown a mercurial thermometer, also 
called pyrometer, for measuring temperatures in flues, breech- 
ings, and chimneys. ‘This instrument is marked for temper- 
atures up to 800° F., though some are graduated for temperatures 
as high as 1,000° F. and are sometimes marked for degrees 
centigrade. These thermometers are very accurate and 
dependable. 

There are also recording thermometers and pyrometers for 
purposes of reference, which record the temperature indications 
on a paper chart continuously, thus showing variations in 
temperature for any given period of time. One of such instru- 
ments is shown in Fig. 18, in which the chart is replaced each 
day by a new one. 

There are different forms and types of thermometers and 
pyrometers made by different manufacturers that may be 
used for ascertaining the temperature of flue gases and fur- 
nace temperature; the few herein described and illustrated 
are representative. 


94. A simple and inexpensive method of obtaining the 
temperature of flue gases, is to suspend in the direct path of the 
gases, for about an hour or so, a vessel containing sand, then to 
remove it and quickly place a high-temperature thermometer 
in the sand. In a few moments the temperature of the sand 
will be indicated on the thermometer scale, and this will prac- 
tically represent the temperature of the escaping gases. 


ELECTRIC PYROMETERS * 


95. When temperatures higher than 1,000° F. are to be 
indicated or recorded, electric pyrometers are used. A diagram- 
matic illustration of an installation consisting of a thermo- 
couple inserted through the furnace wall, and operating an 
indicator near the furnace and also a recording instrument, is 
shown in Fig. 19. 


a 


Gd 


~ th 


§ 25 AND FLUE-GAS ANALYSIS 57 


96. The thermo element consists essentially of two wires, 
or rods, of different materials, which are joined together at 
their extreme ends and exposed to the heat to be measured. 
This end of the thermo-couple as a whole is called the hot junction; 
the other end is called the cold junction, and is connected, by 
suitable wires, to the galvanometer, which is the indicator. 

The two rods of the thermo element are of different electric 
conductivity. If, therefore, the ends of the rods at the hot 
junction are heated, a difference of potential is produced, 
causing an electric current to pass, varying in strength with the 
degree of the thermal difference between the cold and the hot 








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VO 








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TZ 








Fic. 19 


junctions or with the intensity of heat to which the thermo 
element is exposed. 

In each instrument, the relation of the electric current to 
the temperature is accurately determined by experiment, and 
the scale of the indicator is divided to read directly in degrees 
Fahrenheit or centigrade. Just as soon as the thermo element 
is exposed to heat or cold, the electric current produced in 
the two rods actuates the mechanism of the indicator and the 
needle of the latter indicates directly the exact temperature of 
the hot junction, or at the place where the thermo element 
is inserted. 


CARBON-DIOXIDE RECORDERS 


97. Frequently it is desired to obtain continuous samples of 
flue gases and make a record of the carbon-dioxide content of the 
gases on a chart, thus showing for every few minutes in a given 


58 FURNACE EFFICIENCY § 25 


period of time the furnace conditions in terms of carbon- 
dioxide measurement. An apparatus used for this purpose is 
known as a carbon-dioxide, or CO2, recorder, of which there are 
several makes on the market. A CO, recorder produces a 
chart that shows the fluctuations in 
the dioxide content of the gases 
throughout the entire day. Usually 
from seven to eight readings an hour 
are produced on a chart, which gen- 
erally covers a period of 24 hours, 
though a greater number may be 
obtained. 

The operations of CO, recorders 
are performed by rising and falling 
columns of water, and the absorp- 
tion of the dioxide in caustic-potash 
solution. Variations in temperature 
and specific gravity are compensated 
for automatically. 





































98. One of the standard CO, 
recorders is known as the Hays 
automatic Co, and draft re- 
corder, which consists of four 
separate parts, the analyzer, the 
recording gauge, a water-pressure 
regulator, and a combined soot 
filter and condenser. 
=| . By means of a system of tubes 

= |= . and a mercury valve, a definite 

sip quantity of gas is trapped and 
* passed through a vessel containing 

caustic potash in which the carbon 
dioxide of the flue gas is absorbed. The reduction of volume 
shows the exact percentage of dioxide in the sample, and a 
record is made on the chart. Water rises and falls in the tubes, 
and by means of a mercury valve and a water overflow the 
levels of all the liquids are automatically corrected at the end 

































































Fic. 20 


» 


§ 25 AND FLUE-GAS ANALYSIS 59 


of each cycle of analysis. Fig. 20 shows the general appearance 
of the apparatus as a whole. 

This apparatus determines the gas percentages volumetrically. 
A measured volume of gas, 50 cubic centimeters, or about 3 cubic 
inches, is taken. The carbon-dioxide content is absorbed and 
the shrinkage of volume caused by the absorption is recorded 
upon the chart in terms of percentage. It is necessary to the 
proper working of the apparatus that the gas volume taken shall 
not be affected by anything except the absorption process. 

Gases are affected in volume by both pressure and temper- 
ature, and for this reason it is necessary to have both pressure 
and temperature control. The gas sample, when taken by the 
apparatus, is automatically measured at the pressure of the 
atmosphere, and the gas remaining after the absorption of 
the dioxide is automatically measured at the pressure of the 
atmosphere plus the pressure due to a fixed head of water. 
This disposes of any pressure variation that might affect the 
accuracy of the records. 


99. The recording gauge is separate from the analyzer and 
is connected to it with copper tubing, so that the recorder may 
be placed anywhere desired. For example, it may be in the 
engineer’s office while the analyzer is installed in the boiler room, 
power being furnished by running water. A pressure regulator 
is furnished with the apparatus for maintaining a constant 
speed. The motive water may be supplied to the regulator 
from any convenient source, and conducted to the analyzer. 
There are no mechanically operated parts. 

A uniform temperature is essential to accuracy. Because 
of the expansion and contraction of the gases, the gas-measuring 
and gas-absorbing parts are water-jacketed in the same chamber, 
the water being kept in constant circulation in order to insure 
uniform temperature. 


100. A filter is used to remove soot and any other foreign 
matter that may come into the system with the gas. Any 
water vapor that may be in the gases is condensed in the piping 
before they enter the filter. The gases are taken from the last 
pass in the boiler, as near as possible to the point where the 


60 FURNACE EFFICIENCY § 25 


gases leave the heating surfaces, through a 1l-inch pipe, which 
leads direct to the condenser and filter; from the filter the gases 
are carried to the analyzer by a $-inch pipe. 

Caustic potash is used in the apparatus to absorb the carbon 
dioxide. It should be renewed about once each month, because 
otherwise the absorption of the dioxide will not be complete. 
New filtering material should also be put in occasionally. The 
filtering chamber may be filled with broken brick, the pieces 
being about 4 inch in size and thoroughly washed before using. 


101. The general arrangement of the system and the 
relation each part bears to the other is shown diagrammatically 


4 
5 


a] 











H 
af 
1 





Ss '=47 8789 81 OFA 8 


If 
ant us i. 
CEN) Ta To RT 
SE ELE EEE 


wi 


ik re} HE 
LY | eal 





li 
MD oer 
WA 
AN 








Hi 


Fic. 21 


in Fig. 21, in which a is the gas-collecting pipe and b is the soot 
filter. Pipes c and d convey the gas to the analyzer e. The 
recording gauge f is connected to the analyzer by the pipe g, 
and the draft recorder is connected to the back connections of 
the boiler by the pipe h.. The water-supply tank and regulator 
is shown at 7; this tank is connected to the main supply pipe 
by the pipe 7. The pipe k conveys the water from the tank to 
the analyzer, and the pipe ] conveys the waste water from the 


Bus 


§ 25 AND FLUE-GAS ANALYSIS 61 


analyzer. The U-shaped fittings under the soot filter and at 
the junction of the pipes c and d are water-sealed traps, to 
prevent the escape of gas from the system, and also to prevent 
the accumulation of water in the system. 


AUTOMATIC GAS COLLECTORS 


102. Insome steam plants it is desired to obtain an average 
sample of flue gas for a given period of time. For this purpose 
an apparatus known as a gas collector is used. This may be a 
cylindrical tank made of sheet metal, and of about 5 gallons 
capacity. It should be located near the place from which the 
gas is to be taken and be suitably connected with pipes and 
valves. 


103. The principle on which a gas collector operates is as 
follows: The collector is filled with water through suitable 
connections. A certain quantity of ordinary engine oil is 
floated on the surface of the water to prevent the absorption 
of any of the gas, which would otherwise occur and so render 
the sample useless for the purpose in view. After the collector 
is filled with water, the water-supply valve is shut off and the 
drain cock opened; the gas-supply valve is also opened at the 
same time. The drain cock is regulated to empty the collector 
of water in a given time, usually 8 hours, but 1t may be regu- 
lated for any time desired. 

As the water drains out from the collector, the gas flows in 
until the time period is up. Then both the drain cock and the 
gas-supply valve are closed, and connection made between the 
collector and the analyzer by means of a valve and a rubber tube. 

The water-supply valve is again opened; the inflowing water 
now forces out some of the gas into the analyzer until the 
required sample is obtained, when all valves are closed and 
the analysis of the sample made. The sample obtained repre- 
sents an average of the gas for the period collected. 


104. In order to obtain a proper average sample of gas, 
the flow of water from the collector must be constant. If the 
drain cock is not regulated and frequently watched, the flow 

ILT 168—46 


62 | FURNACE EFFICIENCY § 25 


will not be constant, because it will be in proportion to the head 
of water in the collector. The head will vary as the water 
falls, hence the gas will be drawn in faster at the beginning than 
at the end of the sampling period. The outflow of water from 
the collector must be maintained at a uniform rate if the best 
results are to be obtained. 


105. The Hays automatic gas collector, with a 
water-regulating device attached, is shownin Fig. 22. In Fig. 23 
is shown a diagrammatic representation 
of the apparatus, distorted somewhat to 
make clear the principle. It consists of a 
cylindrical tank a of 5 gallons capacity, 
made of sheet metal, and placed upon a 
shelf b. The water-supply valve and con- 
necting pipes are shown at c, and the over- 
flow pipesatd. These are connected at the 
top by a return bend e with a vent hole in 
it to prevent siphoning of the water from 
the collector. The gauge glass f enables 
the observer to see the height of water in the 
collector. The gas-supply valve is at g, 
and the sampling cock at h, to which may 
be connected at will the analyzer by a rub- 
ber tube. The needle valve z controls the 
flow of water into the chamber 7, which 
contains a ‘float regulator k. The drain 
cock and its connecting pipe is shown at l. 











106. The operation of the Hays auto- 
matic gas collector is as follows: First, 
the collector is partly filled with water, and about 1 pint 
of ordinary engine oil introduced, to form a seal on the 
surface of the water to prevent the absorption of some 
of the gas, which would otherwise occur. The water-supply 
valve is opened and the collector allowed to fill until water 
appears at the overflow pipe, when the valve should be closed. 
The drain cock / is opened next and so regulated that the 
collector will empty in the required time which is usually 


Fic. 22 


& 


ie AND FLUE-GAS ANALYSIS 63 


8 hours, but any other period may be chosen, depending on 


individual requirements and conditions. 


107. A constant rate of outflow of water from the collector 
is obtained by the float regulator and its needle-valve arrange- 
ment. When the drain cock / is opened, water flows from the 
collector through the pipe con- 
nection and needle valve into 
the chamber 7, which contains 
the float regulator k. The 
float rises and partly closes the 
needle valve and thus reduces cb 





the inflow of water, until the eget ae 


0000000 000000 00gp 





inflow equals the outflow at 
the drain cock 1. 

The rate of outflow is deter- 
mined by observation of the 
gauge glass attached to the 
collector and by experiment. 
The function of the float regu- 
lator k is to maintain a con- 
stant flow without regard to 
the head of water in the col- 
lector. The outflow of water 
is automatically stopped when 
the level of the water reaches 
a point corresponding with the 
plane of the horizontal pipe 
connecting with and support- 
ing the flow regulator attach- 
ment. This prevents the es- 
cape of the oil from the col- 
lector and insures a trap or seal of water to prevent the 
entrance of air. A discharge at the rate of 1 ounce of water 
per minute will operate the collector for a period of 10 hours. 
The discharge of water from the collector may be throttled to 
operate for any period that may be desired, according to exist- 
ing conditions and requirements of any particular steam plant. 




































































Fic. 23 


64 FURNACE EFFICIENCY § 25 


At the time the drain cock 1 is opened for the outflow of 
water, the gas valve g is opened for the inflow of gas. The gas 
flows in at the same rate as the water flows out. When the 
time period is over for which the apparatus is adjusted, the 
gas analyzer is connected to the gas cock h by a rubber tube, 
and the water valve c is opened, thus admitting water, which 
forces out the gas through the open cock h and rubber tube to 
the gas analyzer. The gas‘is allowed to bubble through the 
analyzer for a few moments and then the gas cock h is shut off 
and the rubber tube disconnected from the analyzer as a matter 
of convenience while an analysis of the sample is being made. 


108. After the analysis has been made, the gas remaining 
in the collector should be allowed to escape to the atmosphere 
by again opening the water-supply valve and filling up the 
collector for another start, and the same cycle of events gone 
through with for the next period, and so on. 


aa & 


5 


FURNACE EFFICIENCY AND 
FLUE-GAS ANALYSIS 





EXAMINATION QUESTIONS 
(1) Define the term efficiency as applied to a steam boiler. 


(2) Why is it difficult to determine the actual efficiency of 
a boiler alone? 


(3) With coal as a fuel, what is the range of boiler efficiency? 


(4) What is required to determine the various heat losses 
in steam boilers? 


(5) What will occur if the supply of air to a boiler furnace 
is insufficient ? 


(6) What is the purpose of a flue-gas analysis? 


(7) With no excess air, what percentages, by volume, will 
result from the complete combustion of 1 pound of carbon? 


(8) What does the heat balance show? 


(9) What chimney temperature may be expected with 
natural draft for good combustion? 


(10) How is the amount of combustible matter in refuse 
determined ? 


(11) Define natural draft. 
(12) Should the ash-pit doors be used to regulate the draft? 


(13) What is the object of employing mechanical draft in 
boiler furnaces? 


§ 25 








CEN UMS 



















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ae In order to do good work, it is very necessary for our students to secure the best 


val ‘4 . > 

© _ / materials, instruments, etc. used in their Courses. We have often found that inexperi- 
Vet” fi enced students have paid exorbitant prices for inferior supplies, and their progress has 
‘\ —s been greatly retarded thereby. To insure our students against such error, arrangements 
4 _ have been made with the Technical Supply Company, of Scranton, Pa., to furnish such as 
: _ desire them with all the supplies necessary in the different Courses. 

Prati (Wa, SEE PRICES ON SEPARATE LIST 





LIGHT-WEIGHT PRINTED ANSWER PAPER 


bes _ 8%"x14". This papes is very tough, durable, and has a fine writing surface. It will last 
> A for years, and the student is thus enabled to keep a permanent record of the work sent to 


the Schools. © aati ; 
I.C.S. COLD-PRESSED DRAWING PAPER 


Size 15”x 20”. Buff color—easy on the eyes. It is unusually strong and tough; takes 


1 x a clean, clear line; is not brittle; is not easily soiled. Best for both ink and pencil. 

9 oe | “TESCO” TRACING CLOTH 

: 3 Used extensively by_draftsmen, architects, engineers, and contractors—a_ high recom: 
“ mendation of quality. It is transparent, strong, free from knots and other imperfections 


and contains no air bubbles. IC.S. instructors assure their students it is thoroughly 
dependable. Furnished in sheets. 15” x 20”. 


PORTFOLIOS 


Cae For keeping your Examination Papers and drawing plates neat and clean and in order. 
yee Don’t roli them up and then forget where they are, or leave them where they will become 
_ . goiled or damaged. Some of these days an employer may ask to see them. 


“TESCO” LIQUID DRAWING INK 


“Tesco” Ink flows smoothly and evenly from the pen and leaves a clear, sharp line of 
aniform intensity, free from cracks and bubbles. 


eos : : - FOUNTAIN PENS 


/ 








c -.. As answers to Examination Questions must be written in ink, you can, with a fountain 
y " -pen, answer your papers any time—anywhere—whether it is in the office, shop, factory, 
| “-<0r home. 


¢ DICTIONARIES 


___ No matter which Course you are studying, no matter what kind of work you do, a 
dictionary is valuable. Keep it near you when you read and when you study. Don’t skip 





the words you don’t understand; look them up, for that is the best way to acquire a 
. yocabulary.- ' 
. att Se)" RUBBER HAND STAMPS 


Stamp your name, address, and class letters and number on every lesson and drawing 
wou send to the Schools. Useful for marking envelopes, books, papers, etc. 


‘eae DRAWING OUTFITS 
The I.C.S. Outfits are not simply “gotten up” to provide something for the student to 
use during his Course. These Outfits will last long after he has gotten into actual work. 
They are practical Outfits—made up from specifications furnished by I.C.S. Instructors. 
Naturally, then, such Outfits must be right. All instruments must be of a_high 
quality to give long and efficient service. All material must be honest, sincere, dependable, 
anfe The busy man cannot be annoyed. with poor material, and the student must not be retarded 
















~ by the use of it. 
ss COMBINATION DRAWING AND STUDY TABLE, 


ee The table is made of oak, and can be folded and placed out of the way; and, althougn 
it weighs but 19%4 pounds, it will-support a direct weight of 200 pounds. The braces are 


_of nickeled rolled steel. : 

chee an - CATALOGS : 
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Supply Co.:; 


Building Trades, Practical Books Relating to Electricity, Practical Books Relating to 
Mechanical and Civil Engineering, Practical Books Relating te Mining, Metallurgy, and 
_ Chemistry. 
Send orders to TECHNICAL SUPPLY COMPANY, Scranton, Pa, 
me: ee « SEE PRICES ON SEPARATE LIST 


‘ j 





PPLIES FOR STUDENTS 


With printed headings especially adapted for use of, students of the I.C.S. Size 


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= awe 


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INSTRUCTION BY MAIL 





